Fix warnings: ex_docmd.c: eval_vars(): Unitialized arg: FP.

Problem    : Uninitialized argument value @ 7704.
Diagnostic : False positive.
Rationale  : Error occurs if `switch(spec_idx)` doesn't enter any case,
             which should not occur after
             `spec_idx = find_cmdline_var(...)` returned non-negative.
Resolution : Add default clause to switch and error if reached.
Fix warnings: ex_eval.c: report_pending(): Np dereference: FP.

Problem    : Dereference of null pointer @ 711.
Diagnostic : False positive.
Rationale  : Codepath producing error invokes this function with values
             `action=RPC_DISCARD, pending=CSTP_FINISH, value=NULL`.
             Now, for some reason, the analyzer is remembering that
             `value` is null, and that `action` is `RPC_DISCARD`, but
             it's not remembering that `pending` is `CSTP_FINISH`.
             Then, it's taking the wrong branch in the switch for
             `pending`. That path would never occur invocating the
             function with those values.
Resolution : Assert function precondition between `pending` and `value`.
             This is, let the compiler know that `value` being null
             implies `pending` not being neither throw neither return.