combo-layer-hook-default.sh: beware of embedded patches

Patching the subject line must be limited to the subject of
the main patch itself. In particular, git formatted patches embedded in the patch must not be changed.

Achieved by limiting the replacement to the lines until the first
subject in the patch, just as it is done for modifying the first
Signed-off-by.

(From OE-Core rev: 2737bd1c3f7c51dd6509a0f91337f695f9c69165)

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/combo-layer-hook-default.sh

@@ -9,5 +9,5 @@ patchfile=$1
 rev=$2
 reponame=$3
 
-sed -i -e "s#^Subject: \[PATCH\] \($reponame: \)*\(.*\)#Subject: \[PATCH\] $reponame: \2#" $patchfile
+sed -i -e "0,/^Subject:/s#^Subject: \[PATCH\] \($reponame: \)*\(.*\)#Subject: \[PATCH\] $reponame: \2#" $patchfile
 sed -i -e "0,/^Signed-off-by:/s#\(^Signed-off-by:.*\)#\($reponame rev: $rev\)\n\n\1#" $patchfile