Changed code to avoid a compiler warning.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402278

dlib/test/array.cpp

@@ -565,7 +565,7 @@ namespace
             }
             for (unsigned long i = 0; i < 100; ++i)
             {
-                unsigned long a;
+                unsigned long a = 0;
                 a1.pop_back(a);
                 DLIB_CASSERT(a == 99-i,"");
             }