gpg4libre: add error string for failed/untrusted encryption

There's one rather common failure mode with gpg, in that untrusted
keys are not accepted by gpgme for encryption.

A user can override that with --trust-model config or cmd line
params, but we can't do much from the gpgme client side:
https://www.gnupg.org/documentation/manuals/gnupg/GPG-Configuration-Options.html

Change-Id: Ia140a7fd25bd3f428aa11a7ceb0b7bdc47b2c900
Reviewed-on: https://gerrit.libreoffice.org/46060Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

include/sfx2/strings.hrc

@@ -169,6 +169,7 @@
 #define RID_SVXSTR_GRFILTER_FILTERERROR         NC_("RID_SVXSTR_GRFILTER_FILTERERROR", "Image filter not found")
 #define RID_SVXSTR_END_REDLINING_WARNING        NC_("RID_SVXSTR_END_REDLINING_WARNING", "This action will exit the change recording mode.\nAny information about changes will be lost.\n\nExit change recording mode?\n\n")
 #define RID_SVXSTR_INCORRECT_PASSWORD           NC_("RID_SVXSTR_INCORRECT_PASSWORD", "Incorrect password")
+#define RID_SVXSTR_GPG_ENCRYPT_FAILURE          NC_("RID_SVXSTR_GPG_ENCRYPT_FAILURE", "OpenPGP key not trusted, damaged, or encryption failure. Please try again.")
 
 #define STR_PASSWD_MIN_LEN                      NC_("STR_PASSWD_MIN_LEN", "(Minimum $(MINLEN) characters)")
 #define STR_PASSWD_MIN_LEN1                     NC_("STR_PASSWD_MIN_LEN1", "(Minimum 1 character)")

sfx2/source/dialog/filedlghelper.cxx

@@ -1534,7 +1534,7 @@ ErrCode FileDialogHelper_Impl::execute( std::vector<OUString>& rpURLList,
                         {
                             ScopedVclPtrInstance< MessageDialog > aBox(
                                 mpPreferredParentWindow,
-                                SfxResId(RID_SVXSTR_INCORRECT_PASSWORD));
+                                SfxResId(RID_SVXSTR_GPG_ENCRYPT_FAILURE));
                             aBox->Execute();
                         }
                     }