fix: segmentation fault, non initialized pointers in dictziplib.hpp

In method void DictData::close() both if (this->chunks) and if (this->offsets) checks can pass even if no allocated memory is assigned to pointers, because both pointers were not initialized to anything, it is UB, so free were called on uninitialized values. Initializing both values to nullptr guarantees that both checks will fail if pointers were not modified, and free is not called.

src/dictziplib.hpp

@@ -42,8 +42,8 @@ private:
     int version;
     int chunkLength;
     int chunkCount;
-    int *chunks;
+    int *chunks = nullptr;
-    unsigned long *offsets; /* Sum-scan of chunks. */
+    unsigned long *offsets = nullptr; /* Sum-scan of chunks. */
     std::string origFilename;
     std::string comment;
     unsigned long crc;