Bazel-Install.bat.tpl: check %BAZEL_VERSION%
Bazel-Install.bat.tpl: check %BAZEL_VERSION%

Bazel-Install-Trigger #792 and
Bazel-Install #16393 failed because
%BAZEL_VERSION% was empty. (Why, I don't know.)

Change-Id: I0d80c72726e436cf4f0e6fcc8e4b666327a8e14c

bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration