FakeVim: Restrict tabstop size

The default minimum of QSpinBox is 0 which is not allowed
for vim's tabstop in general.
It has to be some positive integer.
Beside disallowing the unsupported value it also fixes
some crash which could happen if using the zero as
tabstop width. (div by zero)

Fixes: QTCREATORBUG-28082
Change-Id: I8913b1c28b8ec239ecdf2306fe8861669ccb9d56
Reviewed-by: hjk <hjk@qt.io>

src/plugins/fakevim/fakevimactions.cpp

@@ -114,6 +114,7 @@ FakeVimSettings::FakeVimSettings()
     tabStop.setToolTip(Tr::tr("Vim tabstop option."));
 
 #ifndef FAKEVIM_STANDALONE
+    tabStop.setRange(1, 99);
     backspace.setDisplayStyle(FvStringAspect::LineEditDisplay);
     isKeyword.setDisplayStyle(FvStringAspect::LineEditDisplay);