fix: linuxcncrsh: return PROGRAM NONE if no program is open (2.8)

[adamlouis]

a duplicate of this PR: #2152 .... targetted to 2.8 as suggested by @andypugh

I forked the 2.8 branch of LinuxCNC/linuxcnc and applied the same change.

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I found the following bug while using linuxcncrsh. get program does not return none if no program is open.

The behavior of get program when no program is open is documented as:

program
With get, returns the name of the currently opened program, or "none".

see:

• https://linuxcnc.org/docs/html/man/man1/linuxcncrsh.1.html

• linuxcnc/src/emc/usr_intf/emcrsh.cc

  Line 319 in 8afe6e4

  program

It appears this bug has been present since emcrsh.cc was first committed:

linuxcnc/src/emc/usr_intf/emcrsh.cc

Line 4140 in bf277a0

static cmdResponseType getProgram(char *s)

steps to reproduce:

• run a linuxcnc program with linuxcncrsh
• connect via telnet & init session
• reference:
  • https://github.com/LinuxCNC/linuxcnc/blob/master/tests/linuxcncrsh/test.sh#L29
  • https://linuxcnc.org/docs/html/man/man1/linuxcncrsh.1.html

telnet <SOME_IP> 5007

hello EMC adamlouis 1.1
set enable EMCTOO

• run get program
• run get program
• run get program
• run get program
• run get estop (or any other get * command get machine, get get joint_pos, etc)
• run get program
• run get program
• run get program
• run get program
• ...

expected behavior:

for all commands above:

• get program -> PROGRAM NONE\r\n
• get estop -> ESTOP ON\r\n

actual behavior:

get program --> \r\n
get program --> \r\n\r\n
get program --> \r\n\r\n\r\n
get program --> \r\n\r\n\r\n
get estop --> ESTOP ON\r\n
get program --> ESTOP ON\r\n\r\n
get program --> ESTOP ON\r\n\r\n\r\n
get program --> ESTOP ON\r\n\r\n\r\n\r\n
get program --> ESTOP ON\r\n\r\n\r\n\r\n\r\n

• get program returns the previously executed get * command (except at the start, when no other get has been run)
• each time get program is run while no program is open, an additional new line is added to the response

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In #2152, @andypugh said:

This looks like an obvious bug and I think it should be targetted to 2.8 and then merged up.
(I tried just changing the bae here, but it didn't have the required effect)

[andypugh]

Thanks for this, now pushed to 2.8, 2.9 and master (2.10)