Though it might be legal C/C++, it is indicative a bigger problems. I generally call it 'pointer slopiness'.
See "Do not make assumptions about the result of malloc(0) or calloc(0)", https://www.securecoding.cert.org/confluence/display/seccode/VOID+MEMxx-A.+Do+not+make+assumptions+about+the+result+of+malloc%280%29+or+calloc%280%29.