Skip `NULL` values from `dladdr(3)`

Fixes [Bug #17810]

addr2line.c

@@ -2329,8 +2329,8 @@ rb_dump_backtrace_with_lines(int num_traces, void **traces)
 	    /* if the binary is strip-ed, this may effect */
 	    for (p=dladdr_fbases; *p; p++) {
 		if (*p == info.dli_fbase) {
-		    lines[i].path = info.dli_fname;
+		    if (info.dli_fname) lines[i].path = info.dli_fname;
-		    lines[i].sname = info.dli_sname;
+		    if (info.dli_sname) lines[i].sname = info.dli_sname;
 		    goto next_line;
 		}
 	    }
@@ -2340,9 +2340,11 @@ rb_dump_backtrace_with_lines(int num_traces, void **traces)
 	    obj->base_addr = (uintptr_t)info.dli_fbase;
 	    path = info.dli_fname;
 	    obj->path = path;
-	    lines[i].path = path;
+	    if (path) lines[i].path = path;
+            if (info.dli_sname) {
                 lines[i].sname = info.dli_sname;
                 lines[i].saddr = (uintptr_t)info.dli_saddr;
+            }
 	    strlcpy(binary_filename, path, PATH_MAX);
 	    if (fill_lines(num_traces, traces, 1, &obj, lines, i) == (uintptr_t)-1)
 		break;