Add possibility to require valid keys for a command

Some commands cannot be applied to revoked, expired, or otherwise "bad"
keys. Since this restriction is rather general I decided to add a flag
for this.

GnuPG-bug-id: 6155

src/commands/command.h

@@ -62,6 +62,8 @@ public:
         MustBeTrustedRoot   = 0x0400 | MustBeRoot,
         MustBeUntrustedRoot = 0x0800 | MustBeRoot,
 
+        MustBeValid         = 0x1000, //< key is neither revoked nor expired nor otherwise "bad"
+
         _AllRestrictions_Helper,
         AllRestrictions = 2 * (_AllRestrictions_Helper - 1) - 1
     };

src/view/keylistcontroller.cpp

@@ -58,6 +58,7 @@
 #include "commands/exportpaperkeycommand.h"
 #include "commands/revokekeycommand.h"
 
+#include <Libkleo/Algorithm>
 #include <Libkleo/KeyCache>
 #include <Libkleo/KeyListModel>
 #include <Libkleo/Formatting>
@@ -795,6 +796,12 @@ Command::Restrictions KeyListController::Private::calculateRestrictionsMask(cons
         result |= Command::MustBeCMS;
     }
 
+    if (Kleo::all_of(keys, [](const auto &key) {
+        return !key.isBad();
+    })) {
+        result |= Command::MustBeValid;
+    }
+
     if (all_secret_are_not_owner_trust_ultimate(keys)) {
         result |= Command::MayOnlyBeSecretKeyIfOwnerTrustIsNotYetUltimate;
     }