Fix #13886 nullptr dereference in warningIntToPointerCast() (cppcheck-opensource#7550)

Co-authored-by: chrchr-github <noreply@github.com>

Author: chrchr-github

lib/checkother.cpp

@@ -461,7 +461,7 @@ void CheckOther::warningIntToPointerCast()
             continue;
         if (!tok->valueType() || tok->valueType()->pointer == 0)
             continue;
-        if (!MathLib::isIntHex(from->str()) && from->getKnownIntValue() != 0) {
+        if (!MathLib::isIntHex(from->str()) && from->hasKnownIntValue() && from->getKnownIntValue() != 0) {
             std::string format;
             if (MathLib::isDec(from->str()))
                 format = "decimal";

test/testother.cpp

@@ -2211,6 +2211,10 @@ class TestOther : public TestFixture {
 
         checkIntToPointerCast("uint8_t* ptr = (uint8_t*)0x7000;"); // <- it's common in embedded code to cast address
         ASSERT_EQUALS("", errout_str());
+
+        checkIntToPointerCast("struct S { int i; };\n" // #13886, don't crash
+                              "int f() { return sizeof(((struct S*)0)->i); }");
+        ASSERT_EQUALS("", errout_str());
     }
 
 #define checkInvalidPointerCast(...) checkInvalidPointerCast_(__FILE__, __LINE__, __VA_ARGS__)