improve clarity of fwrite errors (#6792)

Author: MichaelChirico

po/data.table.pot

@@ -2692,12 +2692,12 @@ msgstr ""
 
 #: fwrite.c:909
 #, c-format
-msgid "Can't write gzip header error: %d"
+msgid "Failed to write gzip header. Write returned %d"
 msgstr ""
 
 #: fwrite.c:910
 #, c-format
-msgid "Compress gzip error: %d"
+msgid "Failed to compress gzip. compressbuff() returned %d"
 msgstr ""
 
 #: fwrite.c:911 fwrite.c:928

src/fwrite.c

@@ -906,8 +906,8 @@ void fwriteMain(fwriteMainArgs args)
 #ifndef NOZLIB
         free(zbuffPool);
 #endif
-        if (ret0 == -1) STOP(_("Can't write gzip header error: %d"), ret0);
-        else if (ret1) STOP(_("Compress gzip error: %d"), ret1);
+        if (ret0 == -1) STOP(_("Failed to write gzip header. Write returned %d"), ret0);
+        else if (ret1) STOP(_("Failed to compress gzip. compressbuff() returned %d"), ret1);
         else STOP(_("%s: '%s'"), strerror(errwrite), args.filename);
         // # nocov end
       }