refactor and handle falsy values

Author: archmoj

src/components/drawing/index.js

@@ -485,9 +485,17 @@ drawing.pattern = function(sel, gd, patternID, shape, bgcolor, fgcolor, size, so
             break;
     }
 
+    var str = [
+        shape || 'noSh',
+        bgcolor || 'noBg',
+        fgcolor || 'noFg',
+        size,
+        solidity
+    ].join(';');
+
     var pattern = fullLayout._defs.select('.patterns')
         .selectAll('#' + fullID)
-        .data([shape + ';' + bgcolor + ';' + fgcolor + ';' + size + ';' + solidity], Lib.identity);
+        .data([str], Lib.identity);
 
     pattern.exit().remove();