encoder: Fix int ranges for which BININT1 and BININT2 are emitted

BININT1 emits unsigned integer that fits into 1 byte.
BININT2 emits unsigned integer that fits into 2 bytes.

So they cover [0, 0xff] and [0, 0xffff] ranges including edges. However
we were emitting BININTX opcodes only for numbers being strictly inside
those ranges - i.e. (0, 0xff) and (0, 0xffff) - without edges. As the
result what could be emitted as "K\x00." was emitted as
"J\x00\x00\x00\x00." and so on.

Fix it by emitting BININT1 for [0, 0xff] inclusive and BININT for [0,
0xffff] also inclusive.

encode.go

@@ -440,10 +440,10 @@ func (e *Encoder) encodeInt(k reflect.Kind, i int64) error {
 	// protocol >= 1: BININT*
 	if e.config.Protocol >= 1 {
 		switch {
-		case i > 0 && i < math.MaxUint8:
+		case i >= 0 && i <= math.MaxUint8:
 			return e.emit(opBinint1, byte(i))
 
-		case i > 0 && i < math.MaxUint16:
+		case i >= 0 && i <= math.MaxUint16:
 			return e.emit(opBinint2, byte(i), byte(i >> 8))
 
 		case i >= math.MinInt32 && i <= math.MaxInt32:

fuzz/corpus/test-25e095932ec372c0b51b0c617d2288e794178e77.pickle

+M.
\ No newline at end of file

fuzz/corpus/test-2e5a73ddceb0d2789d380ceb72bc1697a02bebc4.pickle

+I255
+.
\ No newline at end of file

fuzz/corpus/test-318c6bebb228a1524dda5e9e945c99c7a6b45e1d.pickle

+I0
+.
\ No newline at end of file

fuzz/corpus/test-c73e837062d609b296b66ea1c8da973bc896abaa.pickle

+I65535
+.
\ No newline at end of file

fuzz/corpus/test-f303fc511daca7c86d376c6d15863422da312011.pickle

+K.
\ No newline at end of file

ogorek_test.go

@@ -191,14 +191,26 @@ var tests = []TestEntry{
 		P01("I00\n."), // INT 00
 		P2_("\x89.")), // NEWFALSE
 
+	X("int(0)", int64(0),
+		P0("I0\n."),    // INT
+		P1_("K\x00.")), // BININT1
+
 	X("int(5)", int64(5),
 		P0("I5\n."),    // INT
 		P1_("K\x05.")), // BININT1
 
+	X("int(0xff)", int64(0xff),
+		P0("I255\n."),  // INT
+		P1_("K\xff.")), // BININT1
+
 	X("int(0x123)", int64(0x123),
 		P0("I291\n."),      // INT
 		P1_("M\x23\x01.")), // BININT2
 
+	X("int(0xffff)", int64(0xffff),
+		P0("I65535\n."),    // INT
+		P1_("M\xff\xff.")), // BININT2
+
 	X("int(0x12345)", int64(0x12345),
 		P0("I74565\n."),            // INT
 		P1_("J\x45\x23\x01\x00.")), // BININT