renderbuffer: ensure framebuffer gets deleted (#7363)

after commit 4b4971c it uses m_iFbAllocated and deletes if upon calling
release() but Renderbuffer generates directly on m_iFb without calling
alloc() meaning it wont be deleted on release(), set m_iFbAllocated to
true after generating the buffer.

src/render/Renderbuffer.cpp

@@ -35,6 +35,7 @@ CRenderbuffer::CRenderbuffer(SP<Aquamarine::IBuffer> buffer, uint32_t format) :
     glBindRenderbuffer(GL_RENDERBUFFER, 0);
 
     glGenFramebuffers(1, &m_sFramebuffer.m_iFb);
+    m_sFramebuffer.m_iFbAllocated = true;
     m_sFramebuffer.m_vSize        = buffer->size;
     m_sFramebuffer.bind();
     glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, m_iRBO);