panic if templates dir does not exist

[jduepmeier]

If the templates folder does not exist the ls will panic.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x20 pc=0x105854460]

goroutine 67 [running]:
github.com/mrjosh/helm-ls/internal/handler.(*langHandler).LoadDocsOnNewChart.func1({0x14000054740, 0x3f}, {0x0?, 0x0?}, {0x14000054740?, 0x3f?})
  github.com/mrjosh/helm-ls/internal/handler/text_document.go:109 +0x30\npath/filepath.WalkDir({0x14000054740, 0x3f}, 0x14000329f68)
  path/filepath/path.go:530 +0x50\ngit.luolix.top/mrjosh/helm-ls/internal/handler.(*langHandler).LoadDocsOnNewChart(0x140001e7880, {0x1400076e340?, 0x14000346190?})
  github.com/mrjosh/helm-ls/internal/handler/text_document.go:107 +0x84
created by github.com/mrjosh/helm-ls/internal/handler.(*langHandler).NewChartWithInitActions in goroutine 13
  github.com/mrjosh/helm-ls/internal/handler/initialization.go:100 +0xa8

The WalkDir function used here will call the WalkFunc with the error and fs info nil if the directory does not exist (see https://pkg.go.dev/path/filepath#WalkFunc). The current walk function does not check this error and panics.
https://github.com/mrjosh/helm-ls/blob/master/internal/handler/text_document.go#L108