py/vstr: Don't check for byte_len>0 in vstr_ins_blank_bytes.

Having this check takes code size and execution time, and it's not
necessary: all callers of this function pass a non-zero value for
`byte_len` already.  And even if `byte_len` was zero, the code would still
perform correctly.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

py/vstr.c

@@ -188,14 +188,13 @@ char *vstr_ins_blank_bytes(vstr_t *vstr, size_t byte_pos, size_t byte_len) {
     if (byte_pos > l) {
         byte_pos = l;
     }
-    if (byte_len > 0) {
-        // ensure room for the new bytes
-        vstr_ensure_extra(vstr, byte_len);
-        // copy up the string to make room for the new bytes
-        memmove(vstr->buf + byte_pos + byte_len, vstr->buf + byte_pos, l - byte_pos);
-        // increase the length
-        vstr->len += byte_len;
-    }
+    // ensure room for the new bytes
+    vstr_ensure_extra(vstr, byte_len);
+    // copy up the string to make room for the new bytes
+    memmove(vstr->buf + byte_pos + byte_len, vstr->buf + byte_pos, l - byte_pos);
+    // increase the length
+    vstr->len += byte_len;
+    // return a pointer to the location to insert new bytes at
     return vstr->buf + byte_pos;
 }