| Bugfix | |
| * Fix a null pointer dereference when mbedtls_mpi_exp_mod() was called with | |
| A=0 represented with 0 limbs. Up to and including Mbed TLS 2.26, this bug | |
| could not be triggered by code that constructed A with one of the | |
| mbedtls_mpi_read_xxx functions (including in particular TLS code) since | |
| those always built an mpi object with at least one limb. | |
| Credit to OSS-Fuzz. Fixes #4641. |