Fix for Save As dialog when opening a file via command line

When the app was started with a font file passed on the command line,
it would then be impossible to save any changes to a different name,
because the Save As dialog wouldn't open. This was just because we
didn't have a full file path, so we now append the current directory
to the file name that we're given.

Author: j4james

src/main.cpp

@@ -70,7 +70,7 @@ int main(int argc, const char* argv[])
     for (int i = 1; i < argc; i++) {
         auto arg = std::string{argv[i]};
         if (!arg.starts_with("-")) {
-            start_path = arg;
+            start_path = std::filesystem::current_path().append(arg);
             break;
         }
     }