hdview2 root6.12

[faustus123]

This fixes the hdview2 compile error seen with more recent versions of ROOT. The error was seen with v6.12.04, but I think I also saw it with version 6.10.

[gluex]

Test status for this pull request: SUCCESS

Summary: /work/halld/pull_request_test/sim-recon^davidl_hdview2_root6.12/tests/summary.txt Logs: /work/halld/pull_request_test/sim-recon^davidl_hdview2_root6.12/tests/log

Build log: /work/halld/pull_request_test/sim-recon^davidl_hdview2_root6.12/make_davidl_hdview2_root6.12.log Build report: /work/halld/pull_request_test/sim-recon^davidl_hdview2_root6.12/report_davidl_hdview2_root6.12.txt Location of build: /work/halld/pull_request_test/sim-recon^davidl_hdview2_root6.12