panics when there's annotation for a field of an inplace tuple field

[nofun97]

Description

Sysl grammar allows annotations in a field of an inplace tuple.

App:
    !type Tuple:
        a <:
            b <: string:
                @attr = "abc"

But this crashes when there are other annotations with different indentation level.

Steps to Reproduce

Validate the following sysl

App:
    !type Tuple:
        @attr = "abc"
        a <:
            b <: string:
                @attr = "abc"

Expected behavior: Doesn't crash when parsing

Actual behavior:

• Debug&Crash Output

  
  ❯ sysl validate -v test.sysl
  DEBU[0000] Logging: {loglevel:debug verbose:true}
  DEBU[0000] Attempting to load module:test.sysl (root:)
  DEBU[0000] opened file /Users/allanadn/work/github.com/anz-bank/dfa/test.sysl
  DEBU[0000] Parsing: test.sysl
  panic: runtime error: invalid memory address or nil pointer dereference
  [signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x173888c]

goroutine 1 [running]: github.com/anz-bank/sysl/pkg/parse.(TreeShapeListener).applyAnnotations(0xc0000e7680, 0xc0005414b0, 0x1, 0x1) /home/runner/work/sysl/sysl/pkg/parse/listener_impl.go:765 +0x24c github.com/anz-bank/sysl/pkg/parse.(TreeShapeListener).ExitTable(0xc0000e7680, 0xc0006ec440) /home/runner/work/sysl/sysl/pkg/parse/listener_impl.go:739 +0x43c github.com/anz-bank/sysl/pkg/grammar.(TableContext).ExitRule(0xc0006ec440, 0x1be6660, 0xc0000e7680) /home/runner/work/sysl/sysl/pkg/grammar/sysl_parser.go:5365 +0x73 github.com/antlr/antlr4/runtime/Go/antlr.(ParseTreeWalker).ExitRule(0xc0005113c8, 0x1be6660, 0xc0000e7680, 0x2d00f08, 0xc0006ec440) /home/runner/go/pkg/mod/github.com/antlr/antlr4@v0.0.0-20200503195918-621b933c7a7f/runtime/Go/antlr/tree.go:252 +0x77 github.com/antlr/antlr4/runtime/Go/antlr.(ParseTreeWalker).Walk(0xc0005113c8, 0x1be6660, 0xc0000e7680, 0x1bef600, 0xc0006ec440) /home/runner/go/pkg/mod/github.com/antlr/antlr4@v0.0.0-20200503195918-621b933c7a7f/runtime/Go/antlr/tree.go:233 +0x136 github.com/antlr/antlr4/runtime/Go/antlr.(ParseTreeWalker).Walk(0xc0005113c8, 0x1be6660, 0xc0000e7680, 0x1bebdc0, 0xc0005f7350) /home/runner/go/pkg/mod/github.com/antlr/antlr4@v0.0.0-20200503195918-621b933c7a7f/runtime/Go/antlr/tree.go:231 +0xc3 github.com/antlr/antlr4/runtime/Go/antlr.(ParseTreeWalker).Walk(0xc0005113c8, 0x1be6660, 0xc0000e7680, 0x1bebe80, 0xc000601dc0) /home/runner/go/pkg/mod/github.com/antlr/antlr4@v0.0.0-20200503195918-621b933c7a7f/runtime/Go/antlr/tree.go:231 +0xc3 github.com/antlr/antlr4/runtime/Go/antlr.(ParseTreeWalker).Walk(0xc0005113c8, 0x1be6660, 0xc0000e7680, 0x1bef5a0, 0xc0005baf20) /home/runner/go/pkg/mod/github.com/antlr/antlr4@v0.0.0-20200503195918-621b933c7a7f/runtime/Go/antlr/tree.go:231 +0xc3 github.com/anz-bank/sysl/pkg/parse.(Parser).Parse(0xc000511818, 0x7ffeefbff7e1, 0x9, 0x1bf6300, 0xc00000cf80, 0xc00058f838, 0x2, 0x2) /home/runner/work/sysl/sysl/pkg/parse/parse.go:153 +0x1014 github.com/anz-bank/sysl/pkg/parse.LoadAndGetDefaultApp(0x7ffeefbff7e1, 0x9, 0x1bf6300, 0xc00000cf80, 0xc00058f818, 0x1bf6480, 0x24dc460, 0xc0000d2c40, 0x0, 0x0) /home/runner/work/sysl/sysl/pkg/parse/parse.go:671 +0x57 github.com/anz-bank/sysl/pkg/loader.LoadSyslModule(0x0, 0x0, 0x7ffeefbff7e1, 0x9, 0x1bf6480, 0x24dc460, 0xc0000d2c40, 0x1, 0x1, 0x14455b3, ...) /home/runner/work/sysl/sysl/pkg/loader/loader.go:34 +0x342 main.(cmdRunner).Run(0xc000152600, 0x1aa83f2, 0x8, 0x1bf6480, 0x24dc460, 0xc0000d2c40, 0x0, 0x0) /home/runner/work/sysl/sysl/cmd/sysl/cmd_runner.go:39 +0x22c main.main3(0xc0000c4040, 0x4, 0x4, 0x1bf6480, 0x24dc460, 0xc0000d2c40, 0xc0004349c0, 0xc00058ff20) /home/runner/work/sysl/sysl/cmd/sysl/sysl.go:43 +0x307 main.main2(0xc0000c4040, 0x4, 0x4, 0x1bf6480, 0x24dc460, 0xc0000d2c40, 0x1ad8320, 0xc00009e058) /home/runner/work/sysl/sysl/cmd/sysl/sysl.go:88 +0x75 main.main() /home/runner/work/sysl/sysl/cmd/sysl/sysl.go:100 +0x79

### Your Environments
<!---
Run `sysl info` and `sysl env` to show the sysl binary info and related envvars, and paste the result between the ``` marks below.
If you are not running the latest version of sysl, please try upgrading because your issue may have already been fixed.
-->
```sh
❯ sysl info
Build:
  Version      : v0.142.0
  Git Commit   : babc46dce880f94a621a840e69842d3c47497cab
  Date         : 2020-07-15T10:28:01Z
  Go Version   : go1.13.13 linux/amd64
  OS           : darwin/amd64

❯ sysl env
SYSL_MODULES=""
SYSL_PLANTUML="http://www.plantuml.com/plantuml"