forward zlib decompression errors instead of failing hard

lib/mbtiles.js

@@ -231,16 +231,21 @@ MBTiles.prototype.grid = function(x, y, z, callback) {
         function(err, row, rows) {
             if (err) return callback(err);
             if (!row || !row.grid) return callback('Grid does not exist');
-            var grid = zlib.inflate(
-                    !Buffer.isBuffer(row.grid)
-                    ? new Buffer(row.grid, 'binary')
-                    : row.grid
-                ).toString();
-            var data = rows.reduce(function(memo, r) {
-                    memo[r.key_name] = JSON.parse(r.key_json);
-                    return memo;
-                }, {});
-            callback(null, _(JSON.parse(grid)).extend({ data: data }));
+
+            try {
+                var grid = zlib.inflate(
+                           !Buffer.isBuffer(row.grid)
+                           ? new Buffer(row.grid, 'binary')
+                           : row.grid
+                       ).toString();
+                var data = rows.reduce(function(memo, r) {
+                        memo[r.key_name] = JSON.parse(r.key_json);
+                        return memo;
+                    }, {});
+                callback(null, _(JSON.parse(grid)).extend({ data: data }));
+            } catch(err) {
+                callback(err);
+            }
         }
     );
 };