shortest: move some safe code out of exception block

The RevlogError and WdirUnsupported could be raised by
_partialmatch(), but not by the rest of isvalid(), so let's move the
rest out to make it clearer.

Differential Revision: https://phab.mercurial-scm.org/D3458

mercurial/revlog.py

@@ -1506,7 +1506,11 class revlog(object):
             try:
                 if self._partialmatch(test) is None:
                     return False
-
+            except error.RevlogError:
+                return False
+            except error.WdirUnsupported:
+                # single 'ff...' match
+                return True
                 try:
                     i = int(test)
                     # if we are a pure int, then starting with zero will not be
@@ -1517,11 +1521,6 class revlog(object):
                     return False
                 except ValueError:
                     return True
-            except error.RevlogError:
-                return False
-            except error.WdirUnsupported:
-                # single 'ff...' match
-                return True
 
         hexnode = hex(node)
         shortest = hexnode