OpenBLAS

Fix crash in cpuid_riscv64.c

The crash is reproducible when building OpenBLAS without forcing a
target in a riscv64 container running on an X86_64 machine with an
older version of QEMU, e.g., 7.0.0, registered with binfmt_misc to
run riscv64 binaries.  With this setup, cat /proc/cpuinfo in the
container returns the cpu information for the host, which contains a
"model name" string, and we execute the buggy code.  The code in
question is searching in an uninitialised buffer for the ':' character
and doesn't check to see whether it was found or not.  This can result
in pmodel containing the pointer value 1 and a crash when pmodel is
defererenced.  The algorithm to detect the C910V CPU has not been
modified, merely fixed to prevent the crash.

A few additional checks for NULL pointers are added to improve the
robustness of the code and a whitespace error is corrected.