lib,asn1_utils: fix out of bounds access on zero-sized array

* fix error: ... offset 0 is out of the bounds [0, 0] [-Werror=array-bounds]
* fix note: destination object of size 0 allocated by ‘operator new []’
--> data_ = new T[cap_];

lib/include/srsran/asn1/asn1_utils.h

@@ -193,8 +193,12 @@ public:
   {
     size_ = nof_items;
     cap_  = nof_items;
-    data_ = new T[cap_];
-    std::copy(ptr, ptr + size_, data_);
+    if (ptr != NULL) {
+      data_ = new T[cap_];
+      std::copy(ptr, ptr + size_, data_);
+    } else {
+      data_ = NULL;
+    }
   }
   ~dyn_array()
   {