ima_violations.sh: Another fix of condition evaluation

c0c3550 was not enough to fix evaluation against empty
$expected_violations:

ima_violations 1 TINFO: verify open writers violation
/opt/ltp/testcases/bin/ima_violations.sh: line 96: [: 0: unary operator expected

Therefore split checks into two if.

Also improvements (readability)
* shorten line length with saving subtraction into variable
* evaluate empty variable with ${:-}

Fixes: 726ed71 ("ima_violations.sh: Update validate() to support multiple violations")
Link: https://lore.kernel.org/ltp/20251211111046.87297-1-pvorel@suse.cz/
Reported-by: Martin Doucha <mdoucha@suse.cz>
Signed-off-by: Petr Vorel <pvorel@suse.cz>

Author: pevik

testcases/kernel/security/integrity/ima/tests/ima_violations.sh

@@ -87,23 +87,29 @@ validate()
 	local search="$3"
 	local expected_violations="$4"
 	local max_attempt=3
-	local count2 i num_violations_new
+	local count2 diff i num_violations_new pass
 
 	for i in $(seq 1 $max_attempt); do
 		read num_violations_new < $IMA_VIOLATIONS
 		count2="$(get_count $search)"
-		if [ -z "$expected_violations" -a $(($num_violations_new - $num_violations)) -gt 0 ] || \
-		   [ $(($num_violations_new - $num_violations)) -eq $expected_violations ]; then
-			[ -z "$expected_violations" ] && expected_violations=1
+		diff=$(($num_violations_new - $num_violations))
+
+		if [ "$expected_violations" ]; then
+			[ $diff -eq $expected_violations ] && pass=1
+		else
+			[ $diff -gt 0 ] && pass=1
+		fi
+
+		if [ "$pass" = 1 ]; then
 			if [ $count2 -gt $count ]; then
-				tst_res TPASS "$expected_violations $search violation(s) added"
+				tst_res TPASS "${expected_violations:-1} $search violation(s) added"
 				return
 			else
 				tst_res TINFO "$search not found in $LOG ($i/$max_attempt attempt)..."
 				tst_sleep 1s
 			fi
-		elif [ $(($num_violations_new - $num_violations)) -gt 0 ]; then
-			tst_res $IMA_FAIL "$search too many violations added: $num_violations_new - $num_violations"
+		elif [ $diff -gt 0 ]; then
+			tst_res $IMA_FAIL "$search too many violations added: $diff ($num_violations_new - $num_violations)"
 			return
 		else
 			tst_res $IMA_FAIL "$search violation not added"