(svn r27033) -Codechange: Generalize GetTextfile for multiple extensions

- Instead of hardcoding the .txt extension in a printf string, it is
    now stored in an array of possible extensions. This array still only
    contains .txt, so behaviour is unchanged, but this makes it easier
    to add other extensions later.

src/textfile_gui.cpp

@@ -264,12 +264,19 @@ const char *GetTextfile(TextfileType type, Subdirectory dir, const char *filenam
 	char *slash = strrchr(file_path, PATHSEPCHAR);
 	if (slash == NULL) return NULL;
 
-	seprintf(slash + 1, lastof(file_path), "%s_%s.txt", prefix, GetCurrentLanguageIsoCode());
-	if (FioCheckFileExists(file_path, dir)) return file_path;
+	static const char * const exts[] = {
+		"txt",
+	};
+
+	for (size_t i = 0; i < lengthof(exts); i++) {
+		seprintf(slash + 1, lastof(file_path), "%s_%s.%s", prefix, GetCurrentLanguageIsoCode(), exts[i]);
+		if (FioCheckFileExists(file_path, dir)) return file_path;
 
-	seprintf(slash + 1, lastof(file_path), "%s_%.2s.txt", prefix, GetCurrentLanguageIsoCode());
-	if (FioCheckFileExists(file_path, dir)) return file_path;
+		seprintf(slash + 1, lastof(file_path), "%s_%.2s.%s", prefix, GetCurrentLanguageIsoCode(), exts[i]);
+		if (FioCheckFileExists(file_path, dir)) return file_path;
 
-	seprintf(slash + 1, lastof(file_path), "%s.txt", prefix);
-	return FioCheckFileExists(file_path, dir) ? file_path : NULL;
+		seprintf(slash + 1, lastof(file_path), "%s.%s", prefix, exts[i]);
+		if (FioCheckFileExists(file_path, dir)) return file_path;
+	}
+	return NULL;
 }