add download button

app.py

@@ -65,6 +65,7 @@ def molecule(input_pdb):
     allow-scripts allow-same-origin allow-popups 
     allow-top-navigation-by-user-activation allow-downloads" allowfullscreen="" 
     allowpaymentrequest="" frameborder="0" srcdoc='{x}'></iframe>
+    <p><a href="{input_pdb}">download pdb</a></p>
     """
 
 
@@ -76,7 +77,7 @@ def validate(seq):
 def pred_seq(h_seq, l_seq):
     h_seq, l_seq = h_seq.upper(), l_seq.upper()
     h_is_valid, l_is_valid = validate(h_seq), validate(l_seq)
-    if h_is_valid:    
+    if h_is_valid and l_is_valid:    
         sequences = {
             "H": h_seq,
             "L": l_seq