preempt_rt: On initial releases (.0 subver), don't use ksubver and separator for rt patchset

Fixes downloading non-subversioned patchsets

linux-tkg-config/prepare

@@ -690,6 +690,10 @@ _tkg_srcprep() {
         else
           _separator="."
         fi
+        if [[ "${preempt_rt_ksubver}" == 0 ]]; then
+          _separator=
+          preempt_rt_ksubver=
+        fi
         preempt_rt_file_gz="patch-${_basekernel}${_separator}${preempt_rt_ksubver}-rt${_rt_rev_map["$_basekernel"]}.patch.gz"
         preempt_rt_file=`basename ${preempt_rt_file_gz} .gz`
         curl "https://cdn.kernel.org/pub/linux/kernel/projects/rt/${_basekernel}/${preempt_rt_file_gz}" > "$srcdir"/"${preempt_rt_file_gz}"