Stricter validation for popen mode argument on Windows

Context: The ext/standard/tests/file/popen_pclose_error-win32.phpt
test often fails under parallel testing, because the "is not recognized
as an internal or external command" message doesn't actually have a
guaranteed position in the output.

While looking into this, I noticed that this test on Windows tests
something very different (invalid comand) than on Linux (invalid mode).
Here I'm adjusting the Windows popen implementation so it immediately
fails on a `rw` mode, just like it does on Linux.

TSRM/tsrm_win32.c

@@ -468,17 +468,17 @@ TSRM_API FILE *popen_ex(const char *command, const char *type, const char *cwd,
 		return NULL;
 	}
 
-	/*The following two checks can be removed once we drop XP support */
 	type_len = (int)strlen(type);
-	if (type_len <1 || type_len > 2) {
+	if (type_len < 1 || type_len > 2) {
 		return NULL;
 	}
 
-	for (i=0; i < type_len; i++) {
-		if (!(*ptype == 'r' || *ptype == 'w' || *ptype == 'b' || *ptype == 't')) {
-			return NULL;
-		}
-		ptype++;
+	if (ptype[0] != 'r' && ptype[0] != 'w') {
+		return NULL;
+	}
+
+	if (type_len > 1 && (ptype[1] != 'b' && ptype[1] != 't')) {
+		return NULL;
 	}
 
 	cmd = (char*)malloc(strlen(command)+strlen(TWG(comspec))+sizeof(" /c ")+2);

ext/standard/tests/file/popen_pclose_error.phpt

@@ -2,8 +2,8 @@
 Test popen() and pclose function: error conditions
 --SKIPIF--
 <?php
-if(substr(PHP_OS, 0, 3) == 'WIN' || strtoupper( substr(PHP_OS, 0, 3) ) == 'SUN')
-  die("skip Not Valid for Windows & Sun Solaris");
+if (strtoupper( substr(PHP_OS, 0, 3) ) == 'SUN')
+  die("skip Not Valid for Sun Solaris");
 ?>
 --FILE--
 <?php