MANTA-1211/[#99] Fix graph file output issue

A bug was preventing the binary graph file from being written out by
EstimateSVLoci when multi-region is used and no candidate SV content
is found in the targeted regions. Fixed in this patch.

Closes #99.

src/c++/lib/applications/EstimateSVLoci/EstimateSVLoci.cpp

@@ -145,6 +145,7 @@ runESLRegion(
 
     if (! isMultiRegion)
     {
+        // Save the locus set directly in single-region mode to avoid the object copy
         locusFinder.getLocusSet().save(opt.outputFilename.c_str());
     }
     else
@@ -178,7 +179,8 @@ runESL(const ESLOptions& opt)
         runESLRegion(opt, region, mergedSet);
     }
 
-    if (! mergedSet.empty())
+    const bool isMultiRegion(opt.regions.size()>1);
+    if (isMultiRegion)
     {
         mergedSet.save(opt.outputFilename.c_str());
     }