Fix inverted value check in UWP export packager

platform/uwp/export/export.cpp

@@ -517,7 +517,7 @@ Error AppxPackager::add_file(String p_file_name, const uint8_t *p_buffer, size_t
 			int total_out_before = strm.total_out;
 
 			int err = deflate(&strm, Z_FULL_FLUSH);
-			ERR_FAIL_COND_V(err >= 0, ERR_BUG); // Negative means bug
+			ERR_FAIL_COND_V(err < 0, ERR_BUG); // Negative means bug
 
 			bh.compressed_size = strm.total_out - total_out_before;