Ignore tape labels in NDMP code.

When we encounter some sort of tape label in the backup stream
(e.g. FileIndex < 0) then we should just skip that data and not
use the default handling which leads to an EOF. When we now encounter a
unknown data stream we also print an error including the number of the
unwanted datastream.

src/stored/ndmp_tape.c

@@ -431,6 +431,13 @@ static inline bool bndmp_read_data_from_block(JCR *jcr,
          }
       }
 
+      /*
+       * See if we are processing some sort of label?
+       */
+      if (rctx->rec->FileIndex < 0) {
+         continue;
+      }
+
       /*
        * Here we should have read a record from the block which contains some data.
        * Its either:
@@ -460,6 +467,7 @@ static inline bool bndmp_read_data_from_block(JCR *jcr,
          *data_length = 0;
          return true;
       default:
+         Jmsg1(jcr, M_ERROR, 0, _("Encountered an unknown stream type %d\n"), rctx->rec->maskedStream);
          *data_length = 0;
          return true;
       }