try/catch around JSON parse in #getGrid.

lib/mbtiles.js

@@ -218,17 +218,21 @@ MBTiles.prototype.getGrid = function(z, x, y, callback) {
                 : row.grid,
                 function(err,buffer) {
                     if (err) return callback(new Error('Grid is invalid:' + err.message));
-                    var data = rows.reduce(function(memo, r) {
+                    try {
-                        memo[r.key_name] = JSON.parse(r.key_json);
+                        var data = rows.reduce(function(memo, r) {
-                        return memo;
+                            memo[r.key_name] = JSON.parse(r.key_json);
-                    }, {});
+                            return memo;
-                    var result = _(JSON.parse(buffer.toString())).extend({ data: data });
+                        }, {});
+                        var result = JSON.parse(buffer.toString());
+                    } catch(err) {
+                        return callback(new Error('Grid is invalid:' + err.message));
+                    }
                     var options = {
                         'Content-Type': 'text/javascript',
                         'Last-Modified': new Date(that._stat.mtime).toUTCString(),
                         'ETag': that._stat.size + '-' + Number(that._stat.mtime)
                     };
-                    callback(null, result, options);
+                    callback(null, _(result).extend({data:data}), options);
                 });
         }
     );