gopls/internal/cache/parsego: fix OOB crash in fixInitStmt

This is a priori not how to use safetoken. I haven't attempted
to reproduce the crash.

Fixes golang/go#72026

Change-Id: I7a95383032f9a882c8b667203bbe0cf06f85a987
Reviewed-on: https://go-review.googlesource.com/c/tools/+/653596
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>

Author: adonovan

gopls/internal/cache/parsego/parse.go

@@ -528,11 +528,11 @@ func fixInitStmt(bad *ast.BadExpr, parent ast.Node, tok *token.File, src []byte)
 	}
 
 	// Try to extract a statement from the BadExpr.
-	start, end, err := safetoken.Offsets(tok, bad.Pos(), bad.End()-1)
+	start, end, err := safetoken.Offsets(tok, bad.Pos(), bad.End())
 	if err != nil {
 		return false
 	}
-	stmtBytes := src[start : end+1]
+	stmtBytes := src[start:end]
 	stmt, err := parseStmt(tok, bad.Pos(), stmtBytes)
 	if err != nil {
 		return false