bugfix: f.close() only required if open succeeded

when open fails, instead of raising the original error, the "f.close()" was erroring in the final clause.

pipreqs/pipreqs.py

@@ -309,6 +309,7 @@ def parse_requirements(file_):
         logging.error("Failed on file: {}".format(file_))
         raise
     else:
+        try:
             data = [x.strip() for x in f.readlines() if x != "\n"]
         finally:
             f.close()
@@ -375,6 +376,7 @@ def clean(file_, imports):
         logging.error("Failed on file: {}".format(file_))
         raise
     else:
+        try:
             for i in f.readlines():
                 if re_remove.match(i) is None:
                     to_write.append(i)