Fixed #6344 (false positive: out of bounds access when array size is unknown)

lib/checkbufferoverrun.cpp

@@ -568,6 +568,11 @@ void CheckBufferOverrun::checkScope(const Token *tok, const std::vector<std::str
                     const std::size_t ri = indexes.size() - 1 - i;
                     totalIndex += indexes[ri] * totalElements;
                     totalElements *= arrayInfo.num(ri);
+                    if (arrayInfo.num(ri) == -1) {
+                        // unknown size
+                        totalElements = 0;
+                        break;
+                    }
                 }
 
                 // totalElements == 0 => Unknown size

test/testbufferoverrun.cpp

@@ -3409,6 +3409,11 @@ private:
               "}");
         ASSERT_EQUALS("[test.cpp:5]: (error) Array 'f.c[10]' accessed at index 10, which is out of bounds.\n", errout.str());
 
+        check("static const size_t MAX_SIZE = UNAVAILABLE_TO_CPPCHECK;\n"
+              "struct Thing { char data[MAX_SIZE]; };\n"
+              "char f4(const Thing& t) { return !t.data[0]; }");
+        ASSERT_EQUALS("", errout.str());
+
         check("void foo()\n"
               "{\n"
               "char * buf; buf = new char[8];\n"