Fix ./unrealircd hot-patch in case of zero byte patch file.

Such a file is served if the UnrealIRCd version is unaffected.
It printed "This UnrealIRCd version does not require that patch"
but then instead of stopping it continued.. which wasn't all
that bad before GPG/PGP but now it causes failures and scary
warnings.

(See also 035f487684 which
 introduced GPG/PGP)

[skip ci]

unrealircd.in

@@ -274,6 +274,7 @@ elif [ "$1" = "hot-patch" -o "$1" = "cold-patch" ] ; then
 	# A patch file of 0 bytes means the patch is not needed
 	if [ -f patch -a ! -s patch ]; then
 		echo "This UnrealIRCd version does not require that patch"
+		exit 1
 	fi
 
 	wget -O patch.asc "https://www.unrealircd.org/patch?type=$1&patch=$2&version=$UNREALVER&sig=1" || exit 1