mkvinfo: fix null pointer dereference for EbmlBinary data null pointers

Fixes #2072.

NEWS.md

@@ -57,6 +57,8 @@
   claiming that the file had been modified externally when the user wanted to
   save the file once more, requiring a reload of the file losing all
   modifications made since saving the first time.
+* mkvinfo: fixed a null pointer dereference if an `EbmlBinary` element's data
+  pointer is a null pointer. Fixes #2072.
 
 ## Build system changes
 

src/common/strings/formatting.cpp

@@ -287,6 +287,9 @@ std::string
 to_hex(const unsigned char *buf,
        size_t size,
        bool compact) {
+  if (!buf || !size)
+    return {};
+
   static boost::format s_bf_to_hex("0x%|1$02x|");
   static boost::format s_bf_to_hex_compact("%|1$02x|");