run-tests: defer leftover (?) cleanup until after all output is exhausted

Previously, after matching a single line, any contiguous subsequent lines ending
with (?) would be added to the output and removed from the expected output.
This is a problem if the subsequent test output would have matched the consumed
(?) line, because it kept the optional line and then added a duplicate without
the (?) [1].  Instead, wait until there is nothing more to match before handling
the leftovers.

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-February/080197.html

tests/run-tests.py

@@ -1138,12 +1138,11 b' class TTest(Test):'
                     elif warnonly == 1: # Is "not yet" and line is warn only.
                         warnonly = 2 # Yes do warn.
                 break
-
+            else:
             # clean up any optional leftovers
             while expected.get(pos, None):
                 el = expected[pos].pop(0)
-                if not el.endswith(b" (?)\n"):
-                    expected[pos].insert(0, el)
+                    if el and not el.endswith(b" (?)\n"):
                     break
                 postout.append(b'  ' + el)
 

tests/test-run-tests.t

@@ -52,6 +52,12 b' a succesful test'
   >   never happens (?)
   >   xyzzy
   >   nor this (?)
+  >   $ printf 'abc\ndef\nxyz\n'
+  >   123 (?)
+  >   abc
+  >   def (?)
+  >   456 (?)
+  >   xyz
   > EOF
 
   $ rt
@@ -286,6 +292,12 b' Running In Debug Mode'
   xyzzy
   + echo *SALT* 6 0 (glob)
   *SALT* 6 0 (glob)
+  + printf *abc\ndef\nxyz\n* (glob)
+  abc
+  def
+  xyz
+  + echo *SALT* 12 0 (glob)
+  *SALT* 12 0 (glob)
   .
   # Ran 2 tests, 0 skipped, 0 warned, 0 failed.