First check, then convert

tinyxml2.cpp

@@ -1852,12 +1852,12 @@ XMLError XMLDocument::LoadFile( FILE* fp )
         return _errorID;
     }
 
-    const size_t size = filelength;
-    if ( size == 0 ) {
+    if ( filelength == 0 ) {
         SetError( XML_ERROR_EMPTY_DOCUMENT, 0, 0 );
         return _errorID;
     }
 
+    const size_t size = filelength;
     _charBuffer = new char[size+1];
     size_t read = fread( _charBuffer, 1, size, fp );
     if ( read != size ) {