FindCUDA: Make version extraction robust to empty output

I found that `NVCC_OUT` was sometimes empty when I was building.

Modules/FindCUDA.cmake

@@ -926,8 +926,8 @@ mark_as_advanced(CUDA_NVCC_EXECUTABLE)
 if(CUDA_NVCC_EXECUTABLE AND NOT CUDA_VERSION)
   # Compute the version.
   execute_process (COMMAND ${CUDA_NVCC_EXECUTABLE} "--version" OUTPUT_VARIABLE NVCC_OUT)
-  string(REGEX REPLACE ".*release ([0-9]+)\\.([0-9]+).*" "\\1" CUDA_VERSION_MAJOR ${NVCC_OUT})
-  string(REGEX REPLACE ".*release ([0-9]+)\\.([0-9]+).*" "\\2" CUDA_VERSION_MINOR ${NVCC_OUT})
+  string(REGEX REPLACE ".*release ([0-9]+)\\.([0-9]+).*" "\\1" CUDA_VERSION_MAJOR "${NVCC_OUT}")
+  string(REGEX REPLACE ".*release ([0-9]+)\\.([0-9]+).*" "\\2" CUDA_VERSION_MINOR "${NVCC_OUT}")
   set(CUDA_VERSION "${CUDA_VERSION_MAJOR}.${CUDA_VERSION_MINOR}" CACHE STRING "Version of CUDA as computed from nvcc.")
   mark_as_advanced(CUDA_VERSION)
 else()