gemv: call fallback impl in transpose mode with M==0

[ndellingwood]

Address issue #540, problems with degenerate matrix cases when
blas tpls enabled.

[ndellingwood]

Detected with testing on Waterman and Blake testbeds when tpls are enabled (the default case in Trilinos), fix needed for 3.0 release.

[ndellingwood]

Tests now passing in Trilinos integration test builds on waterman.

[brian-kelley]

lgtm

[mhoemmen]

Is the fall-back implementation host-only, or does it do the right thing with device Views?

[ndellingwood]

@mhoemmen it will fallback in either case, I can update it to only do so for host execution.

[ndellingwood]

@mhoemmen fixed with recent commit to not use fallback when Cuda is the exec space, thanks for the catch.

[ndellingwood]

Spot-check passed on kokkos-dev-2:

Running on machine: kokkos-dev-2
Going to test compilers:  gcc/7.3.0 gcc/9.1 intel/18.0.5 clang/8.0 cuda/10.1
Testing compiler gcc/7.3.0
Testing compiler gcc/9.1
  Starting job gcc-7.3.0-OpenMP-release
  Starting job gcc-7.3.0-Pthread-release
  PASSED gcc-7.3.0-Pthread-release
  Starting job gcc-9.1-OpenMP-release
  PASSED gcc-7.3.0-OpenMP-release
Testing compiler intel/18.0.5
  Starting job gcc-9.1-Serial-release
  PASSED gcc-9.1-OpenMP-release
Testing compiler clang/8.0
  Starting job intel-18.0.5-OpenMP-release
  PASSED gcc-9.1-Serial-release
  Starting job clang-8.0-Cuda_OpenMP-release
  PASSED intel-18.0.5-OpenMP-release
Testing compiler cuda/10.1
  Starting job clang-8.0-Pthread_Serial-release
  PASSED clang-8.0-Cuda_OpenMP-release
  PASSED clang-8.0-Pthread_Serial-release
  Starting job cuda-10.1-Cuda_OpenMP-release
  PASSED cuda-10.1-Cuda_OpenMP-release
#######################################################
PASSED TESTS
#######################################################
clang-8.0-Cuda_OpenMP-release build_time=587 run_time=515
clang-8.0-Pthread_Serial-release build_time=240 run_time=334
cuda-10.1-Cuda_OpenMP-release build_time=630 run_time=482
gcc-7.3.0-OpenMP-release build_time=235 run_time=175
gcc-7.3.0-Pthread-release build_time=219 run_time=178
gcc-9.1-OpenMP-release build_time=249 run_time=160
gcc-9.1-Serial-release build_time=227 run_time=174
intel-18.0.5-OpenMP-release build_time=435 run_time=159
#######################################################