add type check for extra_requires on lines 16-18

Author: ynvtlmr

setup.py

@@ -13,6 +13,9 @@
 extra_requirements = open(os.path.join(os.path.dirname(__file__),
             'requirements-testing.txt')).read()
 extra_requires = extra_requirements.strip().split('\n')
+if not isinstance(extra_requires, list):
+    print("requirements-testing.txt was not parsed correctly.")
+    extra_requires = []
 
 
 setup(