Always initialize output values

mypy/private/mypy.py

diff --git a/mypy/private/mypy.py b/mypy/private/mypy.py
index 5a36a88..e5df4bd 100644
--- a/mypy/private/mypy.py
+++ b/mypy/private/mypy.py
@@ -77,6 +77,8 @@
             sys.stderr.write(errors)
             sys.stderr.write(report)
     else:
+        report = ""
+        errors = ""
         status = 0
 
     if output: