MySQL: Empty `where` param makes bogus query.

Added failing MySQL tests for SelectQuery when the `where` is all kinds of empty.
Now it returns `1=1` if nothing else, as suggested by @muka.

lib/dialects/mysql/query-generator.js

@@ -416,7 +416,7 @@ module.exports = (function() {
         result = Utils.format(smth)
       }
 
-      return result
+      return result ? result : '1=1'
     },
 
     hashToWhereConditions: function(hash) {

spec-jasmine/mysql/query-generator.spec.js

@@ -166,6 +166,26 @@ describe('QueryGenerator', function() {
         arguments: ['myTable', {offset: 2}],
         expectation: "SELECT * FROM `myTable`;",
         context: QueryGenerator
+      }, {
+        title: 'multiple where arguments',
+        arguments: ['myTable', {where: {boat: 'canoe', weather: 'cold'}}],
+        expectation: "SELECT * FROM `myTable` WHERE `myTable`.`boat`='canoe' AND `myTable`.`weather`='cold';",
+        context: QueryGenerator
+      }, {
+        title: 'no where arguments (object)',
+        arguments: ['myTable', {where: {}}],
+        expectation: "SELECT * FROM `myTable` WHERE 1;",
+        context: QueryGenerator
+      }, {
+        title: 'no where arguments (string)',
+        arguments: ['myTable', {where: ''}],
+        expectation: "SELECT * FROM `myTable` WHERE 1;",
+        context: QueryGenerator
+      }, {
+        title: 'no where arguments (null)',
+        arguments: ['myTable', {where: null}],
+        expectation: "SELECT * FROM `myTable` WHERE 1;",
+        context: QueryGenerator
       }
     ],