chan_dahdi: Address gcc9 issues

Fixed format-truncation issues in chan_dahdi.c and
sig_analog.c.  Since they're related to fields provided
by dahdi-tools we can't change the buffer sizes so we're just
checking the return from snprintf and printing an errior if we
overflow.

Change-Id: Idc1f3c1565b88a7d145332a0196074b5832864e5

channels/chan_dahdi.c

@@ -7740,8 +7740,16 @@ static struct ast_frame *dahdi_handle_event(struct ast_channel *ast)
 				c++;
 			else
 				c = p->dialdest;
-			if (*c) snprintf(p->dop.dialstr, sizeof(p->dop.dialstr), "M*0%s#", c);
-			else ast_copy_string(p->dop.dialstr,"M*2#", sizeof(p->dop.dialstr));
+
+			if (*c) {
+				int numchars = snprintf(p->dop.dialstr, sizeof(p->dop.dialstr), "M*0%s#", c);
+				if (numchars >= sizeof(p->dop.dialstr)) {
+					ast_log(LOG_WARNING, "Dial string '%s' truncated\n", c);
+				}
+			} else {
+				ast_copy_string(p->dop.dialstr,"M*2#", sizeof(p->dop.dialstr));
+			}
+
 			if (strlen(p->dop.dialstr) > 4) {
 				memset(p->echorest, 'w', sizeof(p->echorest) - 1);
 				strcpy(p->echorest + (p->echotraining / 401) + 1, p->dop.dialstr + strlen(p->dop.dialstr) - 2);

channels/sig_analog.c

@@ -2957,11 +2957,16 @@ static struct ast_frame *__analog_handle_event(struct analog_pvt *p, struct ast_
 			} else {
 				c = p->dialdest;
 			}
+
 			if (*c) {
-				snprintf(p->dop.dialstr, sizeof(p->dop.dialstr), "M*0%s#", c);
+				int numchars = snprintf(p->dop.dialstr, sizeof(p->dop.dialstr), "M*0%s#", c);
+				if (numchars >= sizeof(p->dop.dialstr)) {
+					ast_log(LOG_WARNING, "Dial string '%s' truncated\n", c);
+				}
 			} else {
 				ast_copy_string(p->dop.dialstr,"M*2#", sizeof(p->dop.dialstr));
 			}
+
 			if (strlen(p->dop.dialstr) > 4) {
 				memset(p->echorest, 'w', sizeof(p->echorest) - 1);
 				strcpy(p->echorest + (p->echotraining / 401) + 1, p->dop.dialstr + strlen(p->dop.dialstr) - 2);