Fix handling for complex extensions

This also handles additional input for extensions in case the user
isn't fully aware of how extensions work

jrnl/journals/FolderJournal.py

@@ -17,6 +17,7 @@
 DIGIT_PATTERN = "[0123456789]"
 YEAR_PATTERN = DIGIT_PATTERN * 4
 MONTH_PATTERN = "[01]" + DIGIT_PATTERN
+DAY_PATTERN = "[0-3][0-9]"
 
 DEFAULT_EXTENSION = ".txt"
 
@@ -148,15 +149,15 @@ def _get_month_folders(path: pathlib.Path) -> list[pathlib.Path]:
 
     @staticmethod
     def _get_day_files(path: pathlib.Path, extension: str) -> list[str]:
-        DAY_PATTERN = "[0-3][0-9]" + extension
-        for child in path.glob(DAY_PATTERN):
+        for child in path.glob(DAY_PATTERN + extension):
+            day = str(child.name).replace(extension, '')
             if (
-                int(child.stem) > 0
-                and int(child.stem) <= 31
+                int(day) > 0
+                and int(day) <= 31
                 and time.is_valid_date(
                     year=int(path.parent.name),
                     month=int(path.name),
-                    day=int(child.stem),
+                    day=int(day),
                 )
                 and child.is_file()
             ):