Update src/stdlib_hashmap_chaining.f90

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

Author: chuckyvt

src/stdlib_hashmap_chaining.f90

@@ -345,7 +345,7 @@ module subroutine get_other_chaining_data( map, key, other, exists )
             end if
         else if ( associated( map % inverse(inmap) % target ) ) then
             if (present(exists) ) exists = .true.
-            other = map % inverse(inmap) % target % other
+            allocate(other, source = map % inverse(inmap) % target % other)
         else
             if ( present(exists) ) then
                 exists = .false.