Panic in textDocument/completion in an empty file

[rcjsuen]

Looks like we have a crash if we try to use code completion on an empty file with just a space and we try to invoke code completion on { line: 0, character: 1 }.

goroutine 13 [running]:
runtime/debug.Stack()
	/usr/local/go/src/runtime/debug/stack.go:26 +0x64
runtime/debug.PrintStack()
	/usr/local/go/src/runtime/debug/stack.go:18 +0x1c
github.com/docker/docker-language-server/internal/pkg/server.(*Server).handleRecovered(0x140006d3980, {0x1400003f050, 0x17}, {0x101727d20, 0x1400003f1e8})
	.../internal/pkg/server/server.go:199 +0x44
github.com/docker/docker-language-server/internal/pkg/server.NewServer.func1({0x1400003f050?, 0x14000569467?}, {0x101727d20?, 0x1400003f1e8?})
	.../internal/pkg/server/server.go:127 +0x40
github.com/docker/docker-language-server/internal/tliron/glsp/protocol.(*Handler).Handle.func1()
	.../internal/tliron/glsp/protocol/handler.go:100 +0x6c
panic({0x101727d20?, 0x1400003f1e8?})
	/usr/local/go/src/runtime/panic.go:792 +0x124
github.com/docker/docker-language-server/internal/compose.Completion({0x102195fd0?, 0x10174ef20?}, 0x140005be150, 0x14000704db0, {0x1017f46e8, 0x1400021fb00})
	.../internal/compose/completion.go:148 +0x12e4
github.com/docker/docker-language-server/internal/pkg/server.(*Server).TextDocumentCompletion(0x140006d3980, 0x140000bc000, 0x140005be150)
	.../internal/pkg/server/completion.go:22 +0x228
github.com/docker/docker-language-server/internal/tliron/glsp/protocol.(*Handler).Handle(0x140001ecb48, 0x140000bc000)
	.../internal/tliron/glsp/protocol/handler.go:388 +0x13c8
github.com/docker/docker-language-server/internal/tliron/glsp/server.(*Server).handle(0x14000344cc0, {0x1017eb2f8, 0x14000335f10}, 0x140006cf170, 0x1400056daa0)
	.../internal/tliron/glsp/server/handler.go:48 +0x220
github.com/sourcegraph/jsonrpc2.(*HandlerWithErrorConfigurer).Handle(0x1400054ba20, {0x1017eb2f8, 0x14000335f10}, 0x140006cf170, 0x1400056daa0)
	.../go/pkg/mod/github.com/sourcegraph/[email protected]/handler_with_error.go:21 +0x4c
github.com/sourcegraph/jsonrpc2.(*Conn).readMessages(0x140006cf170, {0x1017eb2f8, 0x14000335f10})
	.../go/pkg/mod/github.com/sourcegraph/[email protected]/conn.go:205 +0x2ac
created by github.com/sourcegraph/jsonrpc2.NewConn in goroutine 1
	.../go/pkg/mod/github.com/sourcegraph/[email protected]/conn.go:62 +0x1d0