Handle self-assignment of some

Don't do anything when pointer is self-assigned.
This resolves possible crashes then something
with reference 1 is being self-assigned and deleted
before referencing once again.

src/shogun/base/some.h

@@ -68,9 +68,11 @@ namespace shogun
     template <typename T>
     Some<T>& Some<T>::operator=(T* other)
     {
-        unref();
-        raw = other;
-        ref();
+        if (raw != other) {
+            unref();
+            raw = other;
+            ref();
+        }
         return *this;
     }
     template <typename T>

tests/unit/base/Some_unittest.cc

@@ -39,6 +39,13 @@ TEST(Some,reassignment)
     EXPECT_EQ(1, kernel->ref_count());
 }
 
+TEST(Some,self_assignment)
+{
+    auto kernel = some<CGaussianKernel>();
+    kernel = kernel;
+    EXPECT_EQ(1, kernel->ref_count());
+}
+
 TEST(Some,get)
 {
     auto kernel = some<CGaussianKernel>();