Makefile.m32: fix to not require OpenSSL with -libssh2 or -rtmp options

Makefile.m32: fix to not require OpenSSL with -libssh2 or -rtmp options

Previously, -libssh2/-rtmp options assumed that OpenSSL is also enabled
(and then failed with an error when not finding expected OpenSSL headers),
but this isn't necessarly true, e.g. when building both libssh2 and curl
against Schannel. This patch makes sure to only enable the OpenSSL backend
with -libssh2/-rtmp, when there was no SSL option explicitly selected.

- Re-implement the logic as a single block of script.
- Also fix an indentation while there.

Assisted-by: Jay Satiro
Closes #7895