patch 8.0.0160: EMSG() is sometimes used where it should be IEMSG()

Problem:    EMSG() is sometimes used for internal errors.
Solution:   Change them to IEMSG(). (Dominique Pelle)  And a few more.
diff --git a/src/eval.c b/src/eval.c
index 70fbc88..11fc035 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -270,7 +270,7 @@
 	p = &vimvars[i];
 	if (STRLEN(p->vv_name) > 16)
 	{
-	    EMSG("INTERNAL: name too long, increase size of dictitem16_T");
+	    IEMSG("INTERNAL: name too long, increase size of dictitem16_T");
 	    getout(1);
 	}
 	STRCPY(p->vv_di.di_key, p->vv_name);