LRF: zero value causes timeout

refs 7956

org.fortiss.af3.platform.raspberry/trunk/lib/src/LaserRangeFinder.c

@@ -88,9 +88,15 @@ GEN_TYPE_int lrf_read() {
                 }
             } else {
                 d = atoi(value);
-                printf("%d\n",d);
-                timeout = 0;
-                return d;
+                if (d != 0) {
+                    printf("%d\n", d);
+                    timeout = 0;
+                    return d;
+                } else {
+                    timeout++;
+                    printf("-1: zero value\n");
+                    return -1;
+                }
             }
         }
     }