iwlwifi: dbg: allow dump collection in case of an early error

Improve the robustness of the dump collection flow in case of an early
error:
1. in iwl_trans_pcie_sync_nmi, disable and enable interrupts only if
   they were already enabled
2. attempt to initiate dump collection in iwl_fw_dbg_error_collect only
   if the device is enabled
3. check Tx command queue was already allocated before trying to collect it

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>