Fix: Wrong initialization of variable modality in X-InstructBLIP's generate() within use_cues statement of joint_video_audio

[globc]

This pull request...

• fixes a wrong initialization of the variable modality within the use_cues statement of X-InstructBLIP's generate() function in joint_video_audio block by moving the modality loop outside.
• adds a missing continue in X-InstructBLIP's forward() function. Currently modality embeddings are appended twice to input if the conditions are met.