declared filename before use

src/output.cpp

@@ -577,6 +577,7 @@ void write_tallies()
     return;
 
   // Set filename for tallies_out
+  std::string filename;
   filename = fmt::format("{}tallies.out", settings::path_output);
 
   // Open the tallies.out file.

src/summary.cpp

@@ -23,6 +23,7 @@ void write_summary()
   write_message("Writing summary.h5 file...", 5);
 
   // Set filename for summary file
+  std::string filename;
   filename = fmt::format("{}summary.h5", settings::path_output);
 
   // Create a new file using default properties.