Fix zoom transforms with non-tiled layers.

Previously, if a zoom transform was used with a non-tiled layer, it could cause
no tiles to be displayed. Now we guarantee that at least one (world-size) tile
is visible.

examples/streets/streets.html

@@ -60,6 +60,7 @@
 
 map.add(po.geoJson()
     .url("streets.json")
+    .zoom(12)
     .size(null)
     .clip(false)
     .on("load", load)
@@ -70,12 +71,10 @@
 }
 
 function load(e) {
-  var width = Math.pow(2, e.tile.zoom - 12);
   for (var i = 0; i < e.features.length; i++) {
     var feature = e.features[i], d = pci(feature);
     if (!feature.element) continue;
     feature.element.setAttribute("stroke", color(d).color);
-    feature.element.setAttribute("stroke-width", width);
     feature.element.appendChild(po.svg("title").appendChild(
         document.createTextNode(feature.data.properties.STREET + ": " + d + " PCI"))
         .parentNode);

src/Layer.js

@@ -57,7 +57,7 @@ po.layer = function(load, unload) {
     c0.column = Math.floor(c0.column);
     c0.row = Math.max(0, Math.floor(c0.row));
     c1.column = Math.floor(c1.column);
-    c1.row = Math.min((1 << (c0.zoom + 8)) / tileSize.y - 1, Math.floor(c1.row));
+    c1.row = Math.max(0, Math.min((1 << (c0.zoom + 8)) / tileSize.y - 1, Math.floor(c1.row)));
 
     // tile-specific projection
     function projection(c) {

src/start.js

@@ -2,4 +2,4 @@ if (!org) var org = {};
 if (!org.polymaps) org.polymaps = {};
 (function(po){
 
-  po.version = "1.0.9"; // semver.org
+  po.version = "1.0.10"; // semver.org