dispatch: don't stack trace on commands like `hg .log`

This used to stack trace because it raised a util.Abort which wasn't
handled in this block. We now handle it. Additionally, we error out
earlier instead of plodding on and showing the "log" entry of the
plain `hg help` output.

mercurial/commands.py

@@ -4020,7 +4020,11 b' def help_(ui, name=None, **opts):'
 
     formatted, pruned = minirst.format(text, textwidth, keep=keep,
                                        section=section)
-    if section and not formatted:
+
+    # We could have been given a weird ".foo" section without a name
+    # to look for, or we could have simply failed to found "foo.bar"
+    # because bar isn't a section of foo
+    if section and not (formatted and name):
         raise util.Abort(_("help section not found"))
 
     if 'verbose' in pruned:

mercurial/dispatch.py

@@ -253,7 +253,7 b' def _runcatch(req):'
             # check if the command is in a disabled extension
             # (but don't check for extensions themselves)
             commands.help_(ui, inst.args[0], unknowncmd=True)
-        except error.UnknownCommand:
+        except (error.UnknownCommand, util.Abort):
             suggested = False
             if len(inst.args) == 2:
                 sim = _getsimilar(inst.args[1], inst.args[0])

tests/test-help.t

@@ -616,6 +616,23 b' Test command without options'
   [255]
 
 
+Make sure that we don't run afoul of the help system thinking that
+this is a section and erroring out weirdly.
+
+  $ hg .log
+  hg: unknown command '.log'
+  (did you mean one of log?)
+  [255]
+
+  $ hg log.
+  hg: unknown command 'log.'
+  (did you mean one of log?)
+  [255]
+  $ hg pu.lh
+  hg: unknown command 'pu.lh'
+  (did you mean one of pull, push?)
+  [255]
+
   $ cat > helpext.py <<EOF
   > import os
   > from mercurial import cmdutil, commands