stdin panics when onCommandCompletion event with colon suffixed command

[lmorg]

Describe the bug:

dev » pacman: foo -f
Error in `pacman` (0,1): Not a valid expression:
                       >     unexpected symbol ':' (58)
                       >     Expression: pacman: foo -f
                       >               :       ^
                       >     Character : 6
                       > Nor a valid statement:
                       >     exec: "pacman": executable file not found in $PATH
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x8 pc=0x1023bf48c]

goroutine 2306 [running]:
github.com/lmorg/murex/builtins/pipes/streams.(*Stdin).GetDataType(0x0)
        /Users/laurencemorgan/Documents/Documents - Laurence’s MacBook Pro/dev/go/src/github.com/lmorg/murex/builtins/pipes/streams/utils.go:41 +0x1c
github.com/lmorg/murex/builtins/core/pipe.cmdMurexNamedPipe(0x14000195df0)
        /Users/laurencemorgan/Documents/Documents - Laurence’s MacBook Pro/dev/go/src/github.com/lmorg/murex/builtins/core/pipe/namedpipe.go:46 +0x14c
github.com/lmorg/murex/lang.executeProcess(0x14000195df0)
        /Users/laurencemorgan/Documents/Documents - Laurence’s MacBook Pro/dev/go/src/github.com/lmorg/murex/lang/process.go:308 +0x804
created by github.com/lmorg/murex/lang.runModeNormal
        /Users/laurencemorgan/Documents/Documents - Laurence’s MacBook Pro/dev/go/src/github.com/lmorg/murex/lang/interpreter_pc.go:79 +0x48

This only happens when a command is using onCommandCompletion PTY

Expected behaviour:
shouldn't panic