[win/asan] GetInstructionSize: Always initialize rel_offset, if given.

Author: bernhardu

compiler-rt/lib/interception/interception_win.cpp

@@ -482,6 +482,11 @@ static const u8 kPrologueWithShortJump2[] = {
 
 // Returns 0 on error.
 static size_t GetInstructionSize(uptr address, size_t* rel_offset = nullptr) {
+
+  if (rel_offset) {
+    *rel_offset = 0;
+  }
+
 #if SANITIZER_ARM64
   // An ARM64 instruction is 4 bytes long.
   return 4;