fix "Can't find internal action" for quote macros when quote replacing is active

[octaeder]

Open Config dialog. In Editor options choose a method for Replace Double Quotes. This will add internal macros
TXS_AUTO_REPLACE_QUOTE_OPEN and TXS_AUTO_REPLACE_QUOTE_CLOSE
to the userMacros list but only after actions have been setup for the (usual) user macros (c.f. ConfigManager::updateUserMacroMenu).

When Config dialog is closed with ok ConfigManager::updateUserMacroShortcuts is executed. It selects each macro from the userMacros list and calls getManagedAction. Obviously this needs to fail for the internal macros mentioned above. Debug messages Can't find internal action are written for both macros.

Also abbreviations come in mind. But debugging LatexCompleter::updateAbbreviations shows that macros are skipped when
macro.abbrev.isEmpty() || macro.snippet().isEmpty() is true. Indeed, this holds for the internal macros because they don't use abbreviations. Since this may not be obvious, it might be reasonable extending the condition in a similar way as this PR does for the shortcuts. Let me know when I should do so.

[sunderme]

no need for the second extension

[sunderme]

thanks