[clang][Interp][NFC] Add missing return statement

I removed the else here, but forgot to add a return before.
Interestingly, none of the existing test cases triggered a problem. A
future commit will add a test case.

clang/lib/AST/Interp/Pointer.cpp

@@ -185,6 +185,7 @@ void Pointer::initialize() const {
       free(Map);
       Map = (InitMap *)-1;
     }
+    return;
   }
 
   // Field has its bit in an inline descriptor.