Improve error handling for invalid applications

If an invalid application name is given (no process matches the name),
we should abort and error out instead of trying to pass bogus arguments
to jmap/jstack.

jdump.sh

@@ -98,7 +98,11 @@ JSTACK="$(which jstack 2>/dev/null)"
 
 [[ -z "$JSTACK" ]] && not_found "jstack"
 
-PID=$($JPS 2>/dev/null | grep -i "$APP_NAME" | awk '{print $1}')
+PID=$($JPS 2>/dev/null | grep -i "$APP_NAME" 2>/dev/null | head -n1 | awk '{print $1}')
+if (( $? > 1 )); then
+    error "Failed to get PID for: $APP_NAME"
+fi
+
 if [[ -z "$PID" ]]; then
     # try again, as root
     if [[ "$USER" != "root" ]]