fix handling of && by htmlentities 'no-double-encode'

expand the test cases

ext/standard/html.c

@@ -1154,7 +1154,7 @@ encode_amp:
 					len += sizeof("&") - 1;
 				} else {
 					char *e = memchr(old + i, ';', oldlen - i);
-					char *s = old + i + 1;
+					char *s = old + i;
 
 					if (!e || (e - s) > 10) { /* minor optimization to avoid "entities" over 10 chars in length */
 						goto encode_amp;

ext/standard/tests/strings/htmlentities18.phpt

@@ -9,6 +9,9 @@ $tests = array(
 	"&; &amp &#a; &9;",
 	"&kffjadfdhsjfhjasdhffasdfas;",
 	"&#8787978789",
+	"&",
+	"&&&",
+	"&ab&&",
 );
 
 foreach ($tests as $test) {
@@ -23,9 +26,15 @@ string(13) "abc&sfdsa"
 string(13) "abc&sfdsa"
 string(33) "test+s & some more D"
 string(33) "test+s & some more D"
-string(20) "&; &amp &#a; &9;"
-string(20) "&; &amp &#a; &9;"
+string(24) "&; &amp &#a; &9;"
+string(24) "&; &amp &#a; &9;"
 string(32) "&kffjadfdhsjfhjasdhffasdfas;"
 string(32) "&kffjadfdhsjfhjasdhffasdfas;"
 string(16) "&#8787978789"
 string(16) "&#8787978789"
+string(5) "&"
+string(5) "&"
+string(15) "&&&"
+string(15) "&&&"
+string(17) "&ab&&"
+string(17) "&ab&&"