desktop: adapt pArgDescr to CommandLineArgs::ParseCommandLine_Impl()

Commit fe5527f1 (desktop, sysui: let
--convert-to imply --headless, 2014-12-22) changed
CommandLineArgs::ParseCommandLine_Impl(), so that --convert-to implies
--headless. However, that worked only when ./soffice.bin was launched;
when the ./soffice wrapper started oosplash, then a logo was still
shown, as oosplash has its own list of switches that disable the splash
screen.

Fix the inconsistency by adding "convert-to" to oosplash's list as well.

Change-Id: I47e30db3b658f179f10e8a447b5d7cea083fcc60

desktop/unx/source/args.c

@@ -38,6 +38,7 @@ static struct {
     { "invisible",  0, 1, 0, 0, 0, NULL },
     { "quickstart", 0, 1, 0, 0, 0, NULL },
     { "minimized",  0, 1, 0, 0, 0, NULL },
+    { "convert-to",  0, 1, 0, 0, 0, NULL },
 
     /* pagein bits */
     { "writer",     0, 0, 0, 0, 0, "pagein-writer"  },