Re #8627. Catch the exception if encountering an unknown monitor.

ADARA files have been seen to occasionally contain 'phantom' monitors that
aren't in the IDF. This was causing the algorithm to fail, but this change
defends against that by catching the exception and then ignoring those
spectra.

Code/Mantid/Framework/Algorithms/src/SumEventsByLogValue.cpp

@@ -331,17 +331,22 @@ namespace Algorithms
     // Loop over the spectra - there will be one per monitor
     for ( std::size_t spec = 0; spec < monitorWorkspace->getNumberHistograms(); ++spec )
     {
-      // Create a column for this monitor
-      const std::string monitorName = monitorWorkspace->getDetector(spec)->getName();
-      auto monitorCounts = outputWorkspace->addColumn("int",monitorName);
-      const IEventList & eventList = monitorWorkspace->getEventList(spec);
-      // Accumulate things in a local vector before transferring to the table workspace
-      std::vector<int> Y(xLength);
-      filterEventList(eventList, minVal, maxVal, log, Y);
-      // Transfer the results to the table
-      for ( int i = 0; i < xLength; ++i )
-      {
-        monitorCounts->cell<int>(i) = Y[i];
+      try {
+        // Create a column for this monitor
+        const std::string monitorName = monitorWorkspace->getDetector(spec)->getName();
+        auto monitorCounts = outputWorkspace->addColumn("int",monitorName);
+        const IEventList & eventList = monitorWorkspace->getEventList(spec);
+        // Accumulate things in a local vector before transferring to the table workspace
+        std::vector<int> Y(xLength);
+        filterEventList(eventList, minVal, maxVal, log, Y);
+        // Transfer the results to the table
+        for ( int i = 0; i < xLength; ++i )
+        {
+          monitorCounts->cell<int>(i) = Y[i];
+        }
+      } catch (Exception::NotFoundError&) {
+        // ADARA-generated nexus files have sometimes been seen to contain 'phantom' monitors that aren't in the IDF.
+        // This handles that by ignoring those spectra.
       }
     }
   }