[Rd] Core dump when calling tclvalue (PR#4724)

[mckay at gmr.com]

Full_Name: Neil McKay
Version: 1.8.0
OS: Linux (RedHat 7.1)
Submission from: (NULL) (129.124.42.210)


I get a core dump when executing the following code:

> library("tcltk")
> zzz<-tclArray()
> tclvalue(zzz)

Running under gdb gives this output:

Program received signal SIGSEGV, Segmentation fault.
makeRTclObject (tclobj=0x0) at tcltk.c:48
48          Tcl_IncrRefCount(tclobj);