patch 8.1.0543: Coverity warns for leaking memory and using wrong struct

Problem:    Coverity warns for leaking memory and using wrong struct.
Solution:   Free pointer when allocation fails. Change "boff" to "loff".
            (closes #3634)

src/ex_getln.c

@@ -1378,6 +1378,7 @@ getcmdline_int(
 			    redrawcmd();
 			    goto cmdline_changed;
 			}
+			vim_free(p);
 		    }
 		}
 		beep_flush();