storage_util: Split preallocate set in storageBackendCreateQemuImgOpts

The only way preallocate could be set is if the info->format was
not RAW (see storageBackendCreateQemuImgSetBacking), so let's just
extract it from the if/else surrounding the application of the
encryption options.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

src/storage/storage_util.c

@@ -831,13 +831,14 @@ storageBackendCreateQemuImgOpts(virStorageEncryptionInfoDefPtr enc,
     } else {
         if (info.encryption)
             virBufferAddLit(&buf, "encryption=on,");
+    }
+
     if (info.preallocate) {
         if (info.size_arg > info.allocation)
             virBufferAddLit(&buf, "preallocation=metadata,");
         else
             virBufferAddLit(&buf, "preallocation=falloc,");
     }
-    }
 
     if (info.nocow)
         virBufferAddLit(&buf, "nocow=on,");