Maintenance: Integers

In TFM and Integer, rshb() shouldn't try to shift a value that is 0.
This leads to using a negative offset to a pointer, but isn't used.

wolfcrypt/src/integer.c

@@ -572,6 +572,8 @@ void mp_rshb (mp_int *c, int x)
     mp_digit r, rr;
     mp_digit D = x;
 
+    if (mp_iszero(c)) return;
+
     /* mask */
     mask = (((mp_digit)1) << D) - 1;
 

wolfcrypt/src/tfm.c

@@ -3174,6 +3174,8 @@ void fp_rshb(fp_int *c, int x)
     fp_digit r, rr;
     fp_digit D = x;
 
+    if (fp_iszero(c)) return;
+
     /* mask */
     mask = (((fp_digit)1) << D) - 1;