Reorganized exception catching in _strip_header() for better code clarity

 - Cleanup suggested by @effigies

Author: kchawla-pi

nipype/utils/spm_docs.py

@@ -51,13 +51,14 @@ def _strip_header(doc):
     cruft = '\x1b'
     try:
         index = doc.index(hdr)
-        index += len(hdr)
-        index += 1
-        doc = doc[index:]
-        try:
-            index = doc.index(cruft)
-        except ValueError:
-            index = len(doc)
-        return doc[:index]
     except ValueError as e:
         raise_from(IOError('This docstring was not generated by Nipype!\n'), e)
+
+    index += len(hdr)
+    index += 1
+    doc = doc[index:]
+    try:
+        index = doc.index(cruft)
+    except ValueError:
+        index = len(doc)
+    return doc[:index]