Fix bug introduced in 5e1fb1dac5

ConflictSet.cpp

@@ -239,9 +239,13 @@ struct Node {
   int8_t partialKeyLen = 0;
   int32_t numChildren = 0;
   Node *parent = nullptr;
-  uint8_t partialKey[kPartialKeyMaxLenEntryPresent];
-  // If not entryPresent, then the partial key might spill over into entry
-  Entry entry;
+  union {
+    uint8_t partialKey[kPartialKeyMaxLenEntryPresent + sizeof(Entry)];
+    struct {
+      uint8_t padding[kPartialKeyMaxLenEntryPresent];
+      Entry entry;
+    };
+  };
   /* end section that's copied to the next node */
 };
 
@@ -1536,8 +1540,13 @@ template <bool kBegin>
   for (;;) {
 
     if ((*self)->partialKeyLen > 0) {
+      const bool wouldBePresent =
+          key.size() <= kPartialKeyMaxLenEntryPresent + int(sizeof(Entry));
       // Handle an existing partial key
       int commonLen = std::min<int>((*self)->partialKeyLen, key.size());
+      if (wouldBePresent) {
+        commonLen = std::min(commonLen, kPartialKeyMaxLenEntryPresent);
+      }
       int partialKeyIndex = longestCommonPrefixPartialKey(
           (*self)->partialKey, key.data(), commonLen);
       if (partialKeyIndex < (*self)->partialKeyLen) {