fix for blank string cases in webgl

lib/get-simple-string.js

@@ -0,0 +1,5 @@
+'use strict';
+
+module.exports = function(a){
+  return (!a && a !== 0) ? '' : a.toString();
+}

lib/glyphs.js

@@ -21,14 +21,14 @@ function getGlyph(symbol, font) {
       textBaseline: "middle",
       lineHeight: 1.0,
       font: font
-    }) 
+    })
   var triSymbol = vectorizeText(symbol, {
       triangles: true,
       textAlign: "center",
       textBaseline: "middle",
       lineHeight: 1.0,
       font: font
-    })
+    }) 
 
   //Calculate bounding box
   var bounds = [[Infinity,Infinity], [-Infinity,-Infinity]]

package.json

@@ -13,6 +13,7 @@
     "gl-vao": "^1.1.2",
     "glslify": "^6.1.0",
     "glsl-out-of-range": "^1.0.2",
+    "is-string-blank": "^1.0.1",
     "typedarray-pool": "^1.0.2",
     "vectorize-text": "^3.0.0"
   },