Merge branch 'strerror_r' into 'master'

Handle zero len for strerror_r

See merge request redox-os/relibc!209

src/header/string/mod.rs

@@ -235,8 +235,10 @@ pub unsafe extern "C" fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: siz
     let len = strlen(msg);
 
     if len >= buflen {
-        memcpy(buf as *mut c_void, msg as *const c_void, buflen - 1);
-        *buf.add(buflen - 1) = 0;
+        if buflen != 0 {
+            memcpy(buf as *mut c_void, msg as *const c_void, buflen - 1);
+            *buf.add(buflen - 1) = 0;
+        }
         return ERANGE as c_int;
     }
     memcpy(buf as *mut c_void, msg as *const c_void, len + 1);

tests/error.c

@@ -19,4 +19,8 @@ int main(void) {
     char buf2[3];
     int ret2 = strerror_r(err, buf2, 3);
     printf("errno: %d = %s, return: %d\n", err, buf2, ret2);
+
+    char buf3[256];
+    int ret3 = strerror_r(err, buf3, 0);
+    printf("errno: %d = %s, return: %d\n", err, buf3, ret3);
 }

tests/expected/error.stdout

 errno: 2 = No such file or directory
 errno: 2 = No such file or directory, return: 0
 errno: 2 = No, return: 34
+errno: 2 = , return: 34