Fix buffer read overflow in ZIP-64 loading code

Don't even try to parse the ZIP-64 header if there is not enough data in
the file.

Credit to OSS-Fuzz: this solves its issue 16250.

src/common/zipstrm.cpp

@@ -1542,6 +1542,8 @@ bool wxZipEndRec::Read(wxInputStream& stream, wxMBConv& conv)
         if (stream.SeekI(z64EndOffset) == wxInvalidOffset)
             return false;
         wxZipHeader dsEnd(stream, Z64_END_SIZE);
+        if ( !dsEnd )
+            return false;
         if ( dsEnd.Read32() != Z64_END_MAGIC ||
             dsEnd.Read64() < Z64_END_SIZE - 12 ) // Check record size
             return false;