imera: protect against NPE in FsSqlDriver#read

    RB: https://rb.dcache.org/r/7385/
    Acked-by: Paul Millar
    Target: trunk
    Request: 2.11 2.10 2.9 2.8 2.7 2.6
(cherry picked from commit f125236)

modules/chimera/src/main/java/org/dcache/chimera/FsSqlDriver.java

@@ -1370,7 +1370,9 @@ int read(Connection dbConnection, FsInode inode, int level, long beginIndex, byt
 
             if (rs.next()) {
                 InputStream in = rs.getBinaryStream(1);
-
+                if (in == null) {
+                    return count;
+                }
                 in.skip(beginIndex);
                 int c;
                 while (((c = in.read()) != -1) && (count < len)) {