Allow "push rbp" as first assembly statement

[Kevin Menard]

When attempting to debug a function, SASM will automatically add mov rbp, rsp as the first statement, unless that's already the first statement. But, a common function preamble is:

push    rbp
mov     rbp, rsp

In this case, SASM unnecessarily adds the mov statement and leads to:

mov     rbp, rsp
push    rbp
mov     rbp, rsp

[Dmitriy Manushin]

Fixed.