fix: Hex editor insert mode inserting or removing too many bytes

lib/libimhex/source/providers/undo/stack.cpp

@@ -80,6 +80,10 @@ namespace hex::prv::undo {
         for (u32 i = 0; i < count; i += 1) {
             i64 index = startIndex + i;
 
+            if (index < 0 || u64(index) >= m_undoStack.size()) {
+                break;
+            }
+
             m_undoStack[index]->undo(m_provider);
             operation->addOperation(std::move(m_undoStack[index]));
         }