[geary/wip/537-send-on-invalid-cc] Composer: Only enable send if CC/BCC/Reply-To are empty or valid

[Michael Gratton <mjog src gnome org>]

commit 840494b2fa79291ded39b7938682498a659428ce
Author: Michael Gratton <mike vee net>
Date:   Sat Aug 17 16:33:29 2019 +1000

    Composer: Only enable send if CC/BCC/Reply-To are empty or valid
    
    Fixes #537

 src/client/composer/composer-widget.vala | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/src/client/composer/composer-widget.vala b/src/client/composer/composer-widget.vala
index e34736e4..3cbc21b6 100644
--- a/src/client/composer/composer-widget.vala
+++ b/src/client/composer/composer-widget.vala
@@ -1765,7 +1765,14 @@ public class ComposerWidget : Gtk.EventBox, Geary.BaseInterface {
     }
 
     private void validate_send_button() {
-        get_action(ACTION_SEND).set_enabled(this.to_entry.valid || this.cc_entry.valid || 
this.bcc_entry.valid);
+        // To must be valid (and hence non-empty), the other email
+        // fields must be either empty or valid.
+        get_action(ACTION_SEND).set_enabled(
+            this.to_entry.valid &&
+            (this.cc_entry.empty || this.cc_entry.valid) &&
+            (this.bcc_entry.empty || this.bcc_entry.valid) &&
+            (this.reply_to_entry.empty || this.reply_to_entry.valid)
+        );
     }
 
     private void set_compact_header_recipients() {