e1000e: prevent null ptr dereference in e1000_tx_queue()
e1000e: prevent null ptr dereference in e1000_tx_queue()

tx_desc can be dereferenced as a null pointer when count is passed in
as 0.

Signed-off-by: Bruce Allan <9ca9a0356a10eed24a8d9ec38dc19d9cd20ba07b@intel.com>
Tested-by: Emil Tantilov <7bb77ce8696ed668ba78a49cc3445dd5ee9fe4b8@intel.com>
Signed-off-by: Jeff Kirsher <87e35f5be20bb3e67f4ba6b86f5f6be3085b1b3a@intel.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas