tools/pydfu.py: Support DFU files with elements of zero size.

Instead of raising a ZeroDivisionError, this tool now just skips any
elements in the DFU file that have zero size.

Signed-off-by: Damien George <damien@micropython.org>

tools/pydfu.py

@@ -521,7 +521,7 @@ def write_elements(elements, mass_erase_used, progress=None):
         data = elem["data"]
         elem_size = size
         elem_addr = addr
-        if progress:
+        if progress and elem_size:
             progress(elem_addr, 0, elem_size)
         while size > 0:
             write_size = size