gtk/unx: remove successive calls to g_main_context_iteration
gtk/unx: remove successive calls to g_main_context_iteration

Replace the sequence:
    non-blocking call to g_main_context_iteration
    if no-event-recvd
        blocking call to g_main_context_iteration
With this one:
    blocking call to g_main_context_iteration until first evt reveived.
This allows more longer sleep period, when nothing is going on (verified
with strace).

Change-Id: I8f4ea911534c90aea091fd68e9f09db11591392f
Reviewed-on: https://gerrit.libreoffice.org/4777
Reviewed-by: Petr Mladek <9cbcfb1260d253e26a699647bd9cbee55818ea4a@suse.cz>
Tested-by: Petr Mladek <9cbcfb1260d253e26a699647bd9cbee55818ea4a@suse.cz>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core