Add missing error condition to stream_context_set_option()

Previously this caused a null pointer dereference if the value
argument was not provided.

Author: nikic

ext/standard/streamsfuncs.c

@@ -1019,6 +1019,10 @@ PHP_FUNCTION(stream_context_set_option)
 			zend_argument_value_error(3, "cannot be null when argument #2 ($wrapper_or_options) is a string");
 			RETURN_THROWS();
 		}
+		if (!zvalue) {
+			zend_argument_value_error(4, "must be provided when argument #2 ($wrapper_or_options) is a string");
+			RETURN_THROWS();
+		}
 
 		RETURN_BOOL(php_stream_context_set_option(context, ZSTR_VAL(wrappername), optionname, zvalue) == SUCCESS);
 	}

ext/standard/tests/streams/stream_context_set_option_error.phpt

@@ -0,0 +1,33 @@
+--TEST--
+stream_context_set_option() error conditions
+--FILE--
+<?php
+
+$ctx = stream_context_create();
+try {
+    stream_context_set_option($ctx, [], "x");
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    stream_context_set_option($ctx, [], null, "x");
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    stream_context_set_option($ctx, "x");
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    stream_context_set_option($ctx, "x", "y");
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+stream_context_set_option(): Argument #3 ($option_name) must be null when argument #2 ($wrapper_or_options) is an array
+stream_context_set_option(): Argument #4 ($value) cannot be provided when argument #2 ($wrapper_or_options) is an array
+stream_context_set_option(): Argument #3 ($option_name) cannot be null when argument #2 ($wrapper_or_options) is a string
+stream_context_set_option(): Argument #4 ($value) must be provided when argument #2 ($wrapper_or_options) is a string