Fix ArraySliceError in complete.d when there is no paren.

[drpriver]

goBackToOpenParen can return size_t.max, which the calling code in getCalltipHint did not handle (and accidentally returns via an out parameter).

Check for this case so we don't get an array slice error.

Before this patch I would get a crash after typing the comma in code like this:

enum Foo {
    X,
}

src/dcd/server/autocomplete/complete.d:366 pure nothrow @nogc @safe dcd.server.autocomplete.complete.CalltipHint dcd.server.autocomplete.complete.getCalltipHint!(std.range.SortedRange!(const(std.experimental.lexer.TokenStructure!(ubyte, "import dparse.lexer:TokenTriviaFields,TriviaToken; mixin TokenTriviaFields;").TokenStructure)[], "a < b", 0).SortedRange).getCalltipHint(std.range.SortedRange!(const(std.experimental.lexer.TokenStructure!(ubyte, "import dparse.lexer:TokenTriviaFields,TriviaToken; mixin TokenTriviaFields;").TokenStructure)[], "a < b", 0).SortedRange, out ulong) [0x1006ebf3f]
src/dcd/server/autocomplete/complete.d:140 dcd.common.messages.AutocompleteResponse dcd.server.autocomplete.complete.complete(const(dcd.common.messages.AutocompleteRequest), ref dsymbol.modulecache.ModuleCache) [0x1006a812b]
src/dcd/server/main.d:337 pure @nogc @safe dcd.common.messages.AutocompleteResponse dcd.server.main.runServer(immutable(char)[][]).__dgliteral66() [0x1006a777b]
src/dcd/server/main.d:362 void dcd.server.main.trySendResponse(std.socket.Socket, lazy dcd.common.messages.AutocompleteResponse, lazy immutable(char)[]) [0x1006a6ecb]
src/dcd/server/main.d:337 int dcd.server.main.runServer(immutable(char)[][]) [0x1006a46f3]
src/dcd/server/main.d:63 _Dmain [0x1006a06a3]

[github-actions[bot]]

Thanks for your Pull Request and making D better!

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[vushu]

thanks! :)