models: be even more defensive when parsing input

also we finally read the documentation for str.find()
https://docs.python.org/3/library/stdtypes.html#str.find

src/teilchensammler_cli/models.py

@@ -37,12 +37,20 @@ async def make_teilchen_input(text: str) -> TeilchenCreate | None:
     import re
     from natsort import natsorted
 
+    text = text.strip()
+
     if not text:
         logger.error("Empty text.")
         return None
 
     name_end = text.find(".")
+    if name_end == -1:  # "." not in text
+        logger.warning("Missing period '.' from text.")
+        logger.debug("Could not find period symbol in input: %s", text)
+        return None
+    else:
         name = text[0:name_end]
+
     if not name:
         logger.error("Could not extract name.")
         logger.debug("Could not extract name from input: %s", text)