patch: simplify Boolean expression slightly

The context variable is either True, False or None. Abbreviate it as C
and we get the following truth table where the second column is the
original expression and the third column is the new expression:

  C     | C or C == None | C is not False
  True  | True           | True
  False | False          | False
  None  | True           | True

mercurial/patch.py

@@ -870,7 +870,7 b' def iterhunks(ui, fp, sourcefile=None):'
             current_hunk = None
             gitworkdone = False
         if ((sourcefile or state == BFILE) and ((not context and x[0] == '@') or
-            ((context or context == None) and x.startswith('***************')))):
+            ((context is not False) and x.startswith('***************')))):
             try:
                 if context == None and x.startswith('***************'):
                     context = True