debug/pe: fix off by one error in valid symbol index test

Fix an off-by-one error in COFFSymbolReadSectionDefAux, specifically
the code that tests whether a symbol index is valid.

Fixes #52525.

Change-Id: I1b6e5dacfd99249c694bef5ae606e90fdb2ef521
Reviewed-on: https://go-review.googlesource.com/c/go/+/402156
Run-TryBot: Than McIntosh <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: thanm

src/debug/pe/symbol.go

@@ -136,10 +136,9 @@ const (
 // auxiliary symbols: https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#auxiliary-symbol-records
 // COMDAT sections: https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#comdat-sections-object-only
 // auxiliary info for section definitions: https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#auxiliary-format-5-section-definitions
-//
 func (f *File) COFFSymbolReadSectionDefAux(idx int) (*COFFSymbolAuxFormat5, error) {
 	var rv *COFFSymbolAuxFormat5
-	if idx < 0 || idx > len(f.COFFSymbols) {
+	if idx < 0 || idx >= len(f.COFFSymbols) {
 		return rv, fmt.Errorf("invalid symbol index")
 	}
 	pesym := &f.COFFSymbols[idx]