修复无activityID时&符号不正确的问题。

@@ -126,7 +126,7 @@ class GroupPurchaseContainer extends Component {
 
         let miniProgramPath;
         if (!activityId) {
-          miniProgramPath = '/pages/group/list?';
+          miniProgramPath = '/pages/group/list';
         } else {
            miniProgramPath = '/pages/group/list?activityId=' + activityId;
         }

@@ -32,8 +32,16 @@ function excludeParams(groupParams, needGender=true){
 
 function joinWxProgramPath(wxPath, groupParams){
     let params = excludeParams(groupParams, false);
+
+    let paramStr = "";
     for(let key in params){
-        wxPath = wxPath + "&" + key + "=" + params[key];
+        paramStr = paramStr + "&" + key + "=" + params[key];
+    }
+
+    if(wxPath.indexOf("?") != -1){
+        wxPath = wxPath + paramStr;
+    }else{
+        wxPath = wxPath + "?" + paramStr.substring(1);
     }
     return wxPath;
 }