exceptions: catch format_exc() exception

Signed-off-by: Ruslan Kuprieiev <[email protected]>

dvc/exceptions.py

@@ -4,5 +4,10 @@ import traceback
 class DvcException(Exception):
     def __init__(self, msg, cause=None):
         self.cause = cause
-        self.cause_tb = traceback.format_exc() if cause else None
+        self.case_tb = None
+        if cause:
+            try:
+                self.cause_tb = traceback.format_exc()
+            except Exception:
+                pass
         super(DvcException, self).__init__(msg)