PVS-Studio warning V547 for DeSmuME

int str_rtrim(char *str, int flags) {
 u32 i=0;

 while (strlen(str)) {
  if ((str[strlen(str)-1] != ' ') ||
   (str[strlen(str)-1] != '\t') ||
   (str[strlen(str)-1] != '\r') ||
   (str[strlen(str)-1] != '\n')) break;
  ...
}

This suspicious code was found in DeSmuME project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression is always true. Probably the '&&' operator should be used here. DeSmuME_VS2005 xstring.cpp 124

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/