Replace improper use of g_malloc(0) with g_new0

Replace improper use of g_malloc(0) with g_new0

Completely remove use of g_malloc (without zeroing of the allocated
memory) and forbid further use.

Replace use of g_malloc0 in cases where the variable holding the pointer
has proper type.

In all of the above cases we can use g_new0 instead.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>