lsp: Fix ast error line index bug (#736)

Signed-off-by: Charlie Egan <charlie@styra.com>

internal/lsp/lint.go

@@ -67,17 +67,16 @@ func updateParse(cache *cache.Cache, uri string) (bool, error) {
 	diags := make([]types.Diagnostic, 0)
 
 	for _, astError := range astErrors {
-		lineLength := 1
-
-		if astError.Location.Row-1 < len(lines) {
-			lineLength = len(lines[astError.Location.Row-1])
-		}
-
 		line := astError.Location.Row - 1
 		if line < 0 {
 			line = 0
 		}
 
+		lineLength := 1
+		if line < len(lines) {
+			lineLength = len(lines[line])
+		}
+
 		key := "regal/parse"
 		link := "https://docs.styra.com/opa/category/rego-parse-error"