Fixed #4523 (false positive: (error) Possible null pointer dereference)

lib/checknullpointer.cpp

@@ -857,6 +857,8 @@ void CheckNullPointer::nullPointerByDeRefAndChec()
                             }
                             back = back->previous();
                         }
+                    } else if (Token::Match(tok1->tokAt(-4), "%varid% = ( * %varid% )", varid)) {
+                        reassign = true;
                     }
 
                     if (reassign) {

test/testnullpointer.cpp

@@ -695,6 +695,12 @@ private:
               "}\n");
         ASSERT_EQUALS("", errout.str());
 
+        check("void f(struct ABC *abc) {\n" // #4523
+              "    abc = (*abc).next;\n"
+              "    if (abc) { }\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
         check("int f(Item *item) {\n"
               "    x = item ? ab(item->x) : 0;\n"
               "    if (item) { }\n"