convert: don't use long list comprehensions

We are iterating over p4changes. Make the continue condition more clear
and easier to add new conditions in future patches, by removing the list
comprehension and move the condition into the existing for-loop.

hgext/convert/p4.py

@@ -126,14 +126,16 b' class p4_source(common.converter_source)'
 
         # handle revision limiting
         startrev = self.ui.config('convert', 'p4.startrev', default=0)
-        self.p4changes = [x for x in self.p4changes
-                          if ((not startrev or int(x) >= int(startrev)) and
-                              (not self.revs or int(x) <= int(self.revs[0])))]
 
         # now read the full changelists to get the list of file revisions
         ui.status(_('collecting p4 changelists\n'))
         lastid = None
         for change in self.p4changes:
+            if startrev and int(change) < int(startrev):
+                continue
+            if self.revs and int(change) > int(self.revs[0]):
+                continue
+
             cmd = "p4 -G describe -s %s" % change
             stdout = util.popen(cmd, mode='rb')
             d = marshal.load(stdout)