Fix Possible Control flow issues (DEADCODE)

Coverity Scan says `Execution cannot reach this statement: "poison_object(v);"`,
so do nothing when `ptr` is always 0 without address_sanitizer.

internal.h

@@ -155,6 +155,14 @@ asan_poison_object(VALUE obj)
     asan_poison_memory_region(ptr, SIZEOF_VALUE);
 }
 
+#if !__has_feature(address_sanitizer)
+#define asan_poison_object_if(ptr, obj) ((void)(ptr), (void)(obj))
+#else
+#define asan_poison_object_if(ptr, obj) do { \
+        if (ptr) asan_poison_object(obj); \
+    } while (0)
+#endif
+
 /*!
  * This function predicates if the given object is fully addressable or not.
  *

iseq.c

@@ -1087,9 +1087,7 @@ remove_coverage_i(void *vstart, void *vend, size_t stride, void *data)
             ISEQ_COVERAGE_SET(iseq, Qnil);
 	}
 
-        if (ptr) {
-            asan_poison_object(v);
-        }
+        asan_poison_object_if(ptr, v);
     }
     return 0;
 }
@@ -3239,9 +3237,7 @@ trace_set_i(void *vstart, void *vend, size_t stride, void *data)
 	    rb_iseq_trace_set(rb_iseq_check((rb_iseq_t *)v), turnon_events);
 	}
 
-        if (ptr) {
-            asan_poison_object(v);
-        }
+        asan_poison_object_if(ptr, v);
     }
     return 0;
 }