stedc scales only if norm is tiny or huge (and not unconditionally)

[angsch]

Description

Replace unconditional scaling https://github.com/Reference-LAPACK/lapack/blob/2cbabee96f05c52e22167d0005c0b3ba08ef37af/SRC/dstedc.f#L380-L387

with conditional scaling as done in, for example, steqr.