No error handling for the backend option

[lumurillo]

If the backend option is not set correctly, there is no error handling. See for examples:

$ gst-launch-1.0 mobilenetv2 name=ynet model-location=/home/mendel/mobilenet_v2_1.0_224/mobilenet_v2_1.0_224.tflite backend=tensorflow backend::input-layer=input  backend::output-layer=MobilenetV2/Predictions/Reshape_1 filesrc location=/usr/share/edgetpudemo/video_stream.mp4 ! decodebin ! videoconvert ! videoscale ! queue ! tee name=t t. ! queue leaky=2 ! videoscale add-borders=true ! queue leaky=2 ! ynet.sink_model t. ! queue leaky=2 ! ynet.sink_bypass ynet.src_bypass ! queue leaky=2 ! detectionoverlay font-scale=0 thickness=2 ! x264enc ! rtspsink service=5000
Caught SIGSEGV
#0  0x0000ffffbd6abdc4 in __waitpid
#1  0x0000ffffbd6eab60 in g_on_error_stack_trace ()
#2  0x0000aaaaca3c5ac0 in  ()
#3  0x0000ffffbda0964c in  ()
#4  0x0000ffffbcd66ea0 in gst_backend_install_properties(GstBackendClass*, r2i::FrameworkCode) (klass=0xaaaae9a83ac0, code=r2i::TENSORFLOW)
#5  0x0000ffffbcd70590 in gst_tensorflow_class_init(GstTensorflowClass*)
#6  0x0000ffffbcd70420 in gst_tensorflow_class_intern_init(gpointer)
#7  0x0000ffffbd82f418 in g_type_class_ref ()
#8  0x0000ffffbd8153f4 in g_object_new_with_properties ()
#9  0x0000ffffbd815d08 in g_object_new ()
#10 0x0000ffffbcd60cc8 in gst_video_inference_set_backend
#11 0x0000ffffbcd62558 in gst_video_inference_set_property
#12 0x0000ffffbd815fc8 in g_object_setv ()
#13 0x0000ffffbd816f54 in g_object_set_property ()
#14 0x0000ffffbd940d20 in  ()
#15 0x0000ffffbd9427d4 in  ()
#16 0x0000ffffbd9434e8 in  ()
#17 0x0000ffffbd93a0c0 in gst_parse_launch_full ()
#18 0x0000ffffbd93a338 in gst_parse_launchv_full ()
#19 0x0000aaaaca3c3774 in  ()
#20 0x0000ffffbd548d24 in __libc_start_main (main=
#21 0x0000aaaaca3c3f74 in  ()
Spinning.  Please run 'gdb gst-launch-1.0 8886' to continue debugging, Ctrl-C to quit, or Ctrl-\ to dump core.