HPCC-31416 CDistributedSuperFile::querySubFile may return incorrect s…

…ubfile

When sub==true and idx is not found, it should throw an exception.
Without this change, the code function did not always throw but dropped
through to return an incorrect subfile.  This incorrect behaviour has
the effect of masking bugs in the code and causing random crashes.

The fix is to ensure an exception is thrown when sub==true and idx is not
found.

Signed-off-by: Shamser Ahmed <shamser.ahmed@lexisnexis.com>

dali/base/dadfs.cpp

@@ -6274,10 +6274,12 @@ class CDistributedSuperFile: public CDistributedFileBase<IDistributedSuperFile>
         if (sub)
         {
             unsigned subfilen = idx;
-            ForEachItemIn(i,subfiles) {
+            ForEachItemIn(i,subfiles)
+            {
                 IDistributedFile &f=subfiles.item(i);
                 IDistributedSuperFile *super = f.querySuperFile();
-                if (super) {
+                if (super)
+                {
                     unsigned ns = super->numSubFiles(true);
                     if (ns>subfilen)
                         return super->querySubFile(subfilen,true);
@@ -6288,7 +6290,8 @@ class CDistributedSuperFile: public CDistributedFileBase<IDistributedSuperFile>
             }
             throw makeStringExceptionV(-1,"CDistributedSuperFile::querySubFile(%u) for superfile %s - subfile doesn't exist ", idx, logicalName.get());
         }
-        return subfiles.item(idx);
+        else
+            return subfiles.item(idx);
     }
 
     virtual IDistributedFile *querySubFileNamed(const char *name, bool sub) override