[Sema] haveSameParameterTypes - replace repeated isNull() test with assertions

As reported on https://pvs-studio.com/en/blog/posts/cpp/0771/ (Snippet 2) - (and mentioned on rGdc4259d5a38409) we are repeating the T1.isNull() check instead of checking T2.isNull() as well, and at this point neither should be null - so we're better off with an assertion.

Differential Revision: https://reviews.llvm.org/D107347

Author: RKSimon

clang/lib/Sema/SemaOverload.cpp

@@ -9586,7 +9586,8 @@ static bool haveSameParameterTypes(ASTContext &Context, const FunctionDecl *F1,
   for (unsigned I = 0; I != NumParams; ++I) {
     QualType T1 = NextParam(F1, I1, I == 0);
     QualType T2 = NextParam(F2, I2, I == 0);
-    if (!T1.isNull() && !T1.isNull() && !Context.hasSameUnqualifiedType(T1, T2))
+    assert(!T1.isNull() && !T2.isNull() && "Unexpected null param types");
+    if (!Context.hasSameUnqualifiedType(T1, T2))
       return false;
   }
   return true;