Fix back() of empty deque in context_mm_black test

The `testPushPop()` test case does a pop out of scope at the end that
lead to UB in `ContextManager::pop()` because it did a `deque::back()`
on an empty deque without checking. This commit adds an assertion in the
`ContextManager` and checks that the test case triggers the assertion.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/context/context_mm.cpp b/src/context/context_mm.cpp
index 2dc2c03bb..ac7d7f8cf 100644
--- a/src/context/context_mm.cpp
+++ b/src/context/context_mm.cpp
@@ -104,6 +104,8 @@ void ContextMemoryManager::push() {
 
 
 void ContextMemoryManager::pop() {
+  Assert(d_nextFreeStack.size() > 0 && d_endChunkStack.size() > 0);
+
   // Restore state from stack
   d_nextFree = d_nextFreeStack.back();
   d_nextFreeStack.pop_back();