Fixing error sentinel for pdftotext when the PDF has no text (scanned images). It was causing a crash previously.

src/paperless_tesseract/parsers.py

@@ -235,6 +235,6 @@ def get_text_from_pdf(pdf_file):
         try:
             pdf = pdftotext.PDF(f)
         except pdftotext.Error:
-            return False
+            return ""
 
     return "\n".join(pdf)