Copy m_nice and m_ioprio values from other in ctor

It appears that when commit 2014073
added the m_ioprio and m_nice member variables that the
constructor was not updated to copy those values.

Fixes Coverity 1028696

Fixes #11626.

Signed-off-by: Paul Harrison <pharrison@mythtv.org>

mythtv/libs/libmythbase/mythsystemlegacy.cpp

@@ -181,6 +181,9 @@ MythSystemLegacy::MythSystemLegacy(const MythSystemLegacy &other) :
     m_args(other.m_args),
     m_directory(other.m_directory),
 
+    m_nice(other.m_nice),
+    m_ioprio(other.m_ioprio),
+
     m_settings(other.m_settings)
 {
     m_semReady.release(other.m_semReady.available());