[clang][bytecode][NFC] Reject invalid FromTypes in emitBuiltinBitcast (#118274)

instead of silently accepting them and failing later.

clang/lib/AST/ByteCode/Compiler.cpp

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 754afff..a95353f 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -6514,6 +6514,8 @@
       return false;
     if (!this->emitGetPtrLocal(TempOffset, E))
       return false;
+  } else {
+    return false;
   }
 
   if (!ToT || ToT == PT_Ptr) {