merge_config.sh: exit on missing input files

Add a check for the existence of input files and exit (with failure)
if they are missing.

Without this additional check, missing files produce error messages
but still result in an output file being generated and a successful
exit code.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/kconfig/merge_config.sh

@@ -100,6 +100,10 @@ cat $INITFILE > $TMP_FILE
 # Merge files, printing warnings on overridden values
 for MERGE_FILE in $MERGE_LIST ; do
 	echo "Merging $MERGE_FILE"
+	if [ ! -r "$MERGE_FILE" ]; then
+		echo "The merge file '$MERGE_FILE' does not exist.  Exit." >&2
+		exit 1
+	fi
 	CFG_LIST=$(sed -n "$SED_CONFIG_EXP" $MERGE_FILE)
 
 	for CFG in $CFG_LIST ; do