Remove throw in zoom evaluation

lib/carto/tree/zoom.js

@@ -21,11 +21,11 @@ tree.Zoom.prototype.eval = function(env) {
         zoom = 0;
 
     if (value > tree.Zoom.maxZoom || value < 0) {
-        throw {
+        env.error({
             message: 'Only zoom levels between 0 and ' +
                 tree.Zoom.maxZoom + ' supported.',
-            index: index
+            index: this.index
-        };
+        });
     }
 
     switch (this.op) {

test/errorhandling/zoommax.mml

@@ -0,0 +1,15 @@
+{
+    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+    "Stylesheet": [
+        "zoommax.mss"
+    ],
+    "Layer": [{
+        "id": "world",
+        "name": "world",
+        "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+        "Datasource": {
+            "file": "http://tilemill-data.s3.amazonaws.com/test_data/shape_demo.zip",
+            "type": "shape"
+        }
+    }]
+}

test/errorhandling/zoommax.mss

@@ -0,0 +1,3 @@
+#world[zoom > 40] {
+  polygon-fill: #fff;
+}

test/errorhandling/zoommax.result

@@ -0,0 +1 @@
+zoommax.mss:1:6 Only zoom levels between 0 and 22 supported.