Resolves: tdf#120175 normalize theme names to our naming scheme

So breeze-dark turns into breeze_dark

Change-Id: Id5d06f73a79f099048b31fd16f9f9611236af392
Reviewed-on: https://gerrit.libreoffice.org/61321
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

icon-themes/README

@@ -24,6 +24,7 @@ How to add a new image set:
          scp2 compilation crashes when using a dash '-'.
          It evidently splits the name into two strings.
    ^ It's probably not true anymore with filelists.
+   ^ if this gets changed, IconThemeSelector::SetPreferredIconTheme needs to change too
 
 - Add its name (new_set) to WITH_THEMES variable in configure.ac
 

vcl/source/app/IconThemeSelector.cxx

@@ -130,7 +130,9 @@ IconThemeSelector::SetUseHighContrastTheme(bool v)
 void
 IconThemeSelector::SetPreferredIconTheme(const OUString& theme, bool bDarkIconTheme)
 {
-    mPreferredIconTheme = theme;
+    // lower case theme name, and (tdf#120175) replace - with _
+    // see icon-themes/README
+    mPreferredIconTheme = theme.toAsciiLowerCase().replace('-','_');
     mPreferDarkIconTheme = bDarkIconTheme;
 }