changing icon sizes no longer emits signal

[Kai Uwe Broulik]

Hi,

> A patch like the one attached seems to help, but someone who knows the KCM
> better (or has time to dig) should make this conditional on the user actually
> changing icon sizes, and only emit for the groups that have changed.

Patch makes sense, though I wonder why we do both emitChange and a 
manual DBus call. From what I gather emitChange does the same.

Plasma-Integration also connects to that signal to update icon sizes.

It looks like a flaw in the previous code, where it would always run 
exportToKDE4() when anything was changed, which would then emit the 
signal, which unbeknownst to me, was also still being used :)

In Plasma 5.17 it used to be:
 > if (m_selectedThemeDirty || m_iconSizesDirty || m_revertIconEffects) {
 >     exportToKDE4();
 > }

So perha