strto(u)l(l): Fix handling of 0x with no hex digits following.

When base is 0 or 16 and the numeric part of the string (after possible leading white space and/or sign) starts with 0x or 0X but is not followed by a hex digit, only the 0 should be taken as part of the subject sequence. Thus, this is not an error condition (errno should not be set), the result should be 0, and if endptr is non-null, *endptr should be set to point to the x or X.

stdlib.asm

@@ -1289,6 +1289,7 @@ db2      cmp   #16                      if the base is 16 then
          cmp   #'X0'
          bne   cn1
 db3      add4  str,#2                       skip them
+         dec   foundOne
          bra   cn1
 db4      cmp   #37                      check for invalid base value
          bge   cn6
@@ -1346,10 +1347,12 @@ cn4      inc4  str                      next char
          bra   cn1
 
 cn5      lda   foundOne                 if no digits were found, flag the error
-         bne   rt1
+         bne   cn7
 cn6      lda   #EINVAL
          sta   >errno
          bra   rt2a
+cn7      bpl   rt1                      if we got a prefix but no more digits
+         dec4  str                        the subject sequence ends with the 0
 ;
 ;  return the results
 ;
@@ -1636,6 +1639,7 @@ db2      cmp   #16                      if the base is 16 then
          cmp   #'X0'
          bne   cn1
 db3      add4  str,#2                       skip them
+         dec   foundOne
          bra   cn1
 db4      cmp   #37                      check for invalid base value
          jge   cn6
@@ -1691,10 +1695,12 @@ cn4      inc4  str                      next char
          bra   cn1
 
 cn5      lda   foundOne                 if no digits were found, flag the error
-         bne   rt1
+         bne   cn7
 cn6      lda   #EINVAL
          sta   >errno
          bra   rt2a
+cn7      bpl   rt1                      if we got a prefix but no more digits
+         dec4  str                        the subject sequence ends with the 0
 ;
 ;  return the results
 ;