nanopb vulnerabilities (OSS-Fuzz)

3 vulnerabilities.

• nanopb OSS-Fuzz Heap-buffer-overflow in allocate_field OSV-2020-1567 Fix available No scoreAugust 2, 2020
• nanopb OSS-Fuzz Heap-buffer-overflow in allocate_field OSV-2020-1565 Fix available No scoreAugust 2, 2020
• nanopb OSS-Fuzz Use-of-uninitialized-value in pb_encode_varint OSV-2020-1564 Fix available No scoreAugust 2, 2020