Merge pull request #8921 from TimothyZhang/fix-program-cache-add

release old program with the same key before adding glprogram

cocos/renderer/CCGLProgramCache.cpp

@@ -432,9 +432,16 @@ GLProgram* GLProgramCache::getGLProgram(const std::string &key)
 
 void GLProgramCache::addGLProgram(GLProgram* program, const std::string &key)
 {
+    // release old one
+    auto prev = getProgram(key);
+    if( prev == program )
+        return;
+
+    _programs.erase(key);
+    CC_SAFE_RELEASE_NULL(prev);
+
     if (program)
-        program->retain();
-    
+        program->retain();    
     _programs[key] = program;
 }