Add an assertion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107645 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Checker/VLASizeChecker.cpp b/lib/Checker/VLASizeChecker.cpp
index dfb606b..b25843c 100644
--- a/lib/Checker/VLASizeChecker.cpp
+++ b/lib/Checker/VLASizeChecker.cpp
@@ -121,6 +121,9 @@
   DefinedOrUnknownSVal SizeIsKnown = SV.EvalEQ(state, Extent, ArraySize);
   state = state->Assume(SizeIsKnown, true);
 
+  // Assume should not fail at this point.
+  assert(state);
+
   // Remember our assumptions!
   C.addTransition(state);
 }