detailer: skip blank lines when building the fallback prompt pool

A blank spacer line between a [CLASS=...] line and a plain fallback
line (common when formatting the prompt for readability) was being
counted as an empty fallback entry, silently pushing the real fallback
text out of position and handing untagged detections an empty prompt.

modules/detailer/helper.py

@@ -50,6 +50,8 @@ def parse_prompt_lines(text: str):
     fallback: list[str] = []
     for line in (text or '').split('\n'):
         line = line.strip()
+        if len(line) == 0:
+            continue # blank spacer lines don't count as a fallback entry
         m = class_tag_re.match(line)
         if m:
             names = [n.strip().lower() for n in m.group(1).split(',') if n.strip()]