JS: fix minifying strings where the last character needs to be escape…

…d as we change the quotes

js/js_test.go

@@ -179,6 +179,7 @@ func TestJS(t *testing.T) {
 		{`"a"+"b"+5+"c"+"d"`, `"ab"+5+"cd"`},
 		{`"a"+"b"+5+6+"d"`, `"ab"+5+6+"d"`},
 		{"`$${foo}`", "`$${foo}`"},
+		{"'\\n\\nCheck the render method of `'", "`\n\nCheck the render method of \\``"},
 
 		// rename true, false, undefined, Infinity
 		{`x=true`, `x=!0`},

js/util.go

@@ -1023,7 +1023,7 @@ func replaceEscapes(b []byte, quote byte, prefix, suffix int) []byte {
 	// strip unnecessary escapes
 	j := 0
 	start := 0
-	for i := prefix; i < len(b)-suffix-1; i++ {
+	for i := prefix; i < len(b)-suffix; i++ {
 		if c := b[i]; c == '\\' {
 			c = b[i+1]
 			if c == quote || c == '\\' || quote != '`' && (c == 'n' || c == 'r') || c == '0' && (len(b)-suffix <= i+2 || b[i+2] < '0' || '7' < b[i+2]) {