Fixed nil pointer exception in `upload` (regression)

[cmaglie]

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• [X] Tests for the changes have been added (for bug fixes / features)
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• [ ] UPGRADING.md has been updated with a migration guide (for breaking changes)
• [ ] configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Running an upload outside of a sketch with the --input-dir flag will result in a nil pointer exception. This PR fixed it.

What is the current behavior?

~/Arduino/Blink$ arduino-cli upload -b arduino:mbed_opta:opta -i build/Blink.ino.bin -t -p /dev/cu.usbmodem11301 --dry-run -v
Esecuzione di un touch reset a 1200-bps sulla porta seriale /dev/cu.usbmodem11301
In attesa della porta di caricamento...
Non è stata trovata alcuna porta di upload, come alternativa verrà utilizzata /dev/cu.usbmodem11301
"/home/cmaglie/.arduino15/packages/arduino/tools/dfu-util/0.10.0-arduino1/dfu-util" --device 0x2341:0x0364 -D "build/Blink.ino.bin" -a0 --dfuse-address=0x08040000:leave
Nuova porta di caricamento: /dev/cu.usbmodem11301 (serial)
~/Arduino/Blink$ cd ..
~/Arduino$ arduino-cli upload -b arduino:mbed_opta:opta -i Blink/build/Blink.ino.bin -t -p /dev/cu.usbmodem11301 --dry-run -v
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x68 pc=0xc56765]

goroutine 1 [running]:
github.com/arduino/arduino-cli/internal/arduino/sketch.(*Sketch).GetDefaultProgrammer(...)
    /home/cmaglie/Workspace/arduino-cli/internal/arduino/sketch/sketch.go:252
github.com/arduino/arduino-cli/commands/upload.Upload({0x19a5be0?, 0x0?}, 0xc000531ba8, {0x127afc0, 0xc000013728}, {0x127afc0, 0xc000013740})
    /home/cmaglie/Workspace/arduino-cli/commands/upload/upload.go:154 +0x345
github.com/arduino/arduino-cli/internal/cli/upload.runUploadCommand({0xc0003ba120, 0x0, 0x0?}, 0xc000398750)
    /home/cmaglie/Workspace/arduino-cli/internal/cli/upload/upload.go:201 +0xc1f
github.com/arduino/arduino-cli/internal/cli/upload.NewCommand.func2(0xc0003a3b00?, {0xc0003ba120?, 0x4?, 0xf22d11?})
    /home/cmaglie/Workspace/arduino-cli/internal/cli/upload/upload.go:68 +0x2b
github.com/spf13/cobra.(*Command).execute(0xc0003a3b00, {0xc0003ba090, 0x9, 0x9})
    /home/cmaglie/Software/go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:987 +0xaa3
github.com/spf13/cobra.(*Command).ExecuteC(0xc000188300)
    /home/cmaglie/Software/go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1115 +0x3ff
github.com/spf13/cobra.(*Command).Execute(0x0?)
    /home/cmaglie/Software/go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1039 +0x13
main.main()
    /home/cmaglie/Workspace/arduino-cli/main.go:31 +0x74

What is the new behavior?

~/Arduino/Blink$ arduino-cli upload -b arduino:mbed_opta:opta -i build/Blink.ino.bin -t -p /dev/cu.usbmodem11301 --dry-run -v
Esecuzione di un touch reset a 1200-bps sulla porta seriale /dev/cu.usbmodem11301
In attesa della porta di caricamento...
Non è stata trovata alcuna porta di upload, come alternativa verrà utilizzata /dev/cu.usbmodem11301
"/home/cmaglie/.arduino15/packages/arduino/tools/dfu-util/0.10.0-arduino1/dfu-util" --device 0x2341:0x0364 -D "build/Blink.ino.bin" -a0 --dfuse-address=0x08040000:leave
Nuova porta di caricamento: /dev/cu.usbmodem11301 (serial)
~/Arduino/Blink$ cd ..
~/Arduino$ arduino-cli upload -b arduino:mbed_opta:opta -i Blink/build/Blink.ino.bin -t -p /dev/cu.usbmodem11301 --dry-run -v
Esecuzione di un touch reset a 1200-bps sulla porta seriale /dev/cu.usbmodem11301
In attesa della porta di caricamento...
Non è stata trovata alcuna porta di upload, come alternativa verrà utilizzata /dev/cu.usbmodem11301
"/home/cmaglie/.arduino15/packages/arduino/tools/dfu-util/0.10.0-arduino1/dfu-util" --device 0x2341:0x0364 -D "Blink/build/Blink.ino.bin" -a0 --dfuse-address=0x08040000:leave
Nuova porta di caricamento: /dev/cu.usbmodem11301 (serial)

Does this PR introduce a breaking change, and is titled accordingly?

Other information

[manchoz]

Issue fixed.

Thanks!