src/main: free_status_print(): free slots hash table only if existing
src/main: free_status_print(): free slots hash table only if existing

Otherwise this leads to an assertion error in g_hash_table_destroy()
when RaucStatusPrint population was aborted early, e.g. due to missing
access to D-Bus.

Signed-off-by: Enrico Joerns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

ejoerns/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,ejoerns/rauc