e_init crashes if EPIPHANY_HOME is not set; possible buffer overrun as well

[Urhixidur]

e_init(char *hdf) misbehaves if the EPIPHANY_HOME environment variable is not set.

Looking in epiphany-hal.c, we see the fetch of hdf_env_var_name (set to "EPIPHANY_HDF") is guarded, whereas the following fetch of esdk_path (set to "EPIPHANY_HOME") is not. If esdk_env is NULL, strncpy() is called on a NULL src argument, a case which is not even mentioned in the strncpy man pages.

A secondary issue is the strncat used to build the platform.hdf path. Its n argument is too large and can potentially lead to a buffer overflow.

See https://parallella.org/forums/viewtopic.php?f=13&t=2544&p=14462#p14462 for proposed fixes.