tests: Add XPath fuzzing

Only fuzz the parser for now.

tests/data_fuzz_xpath/basic.xpath

@@ -0,0 +1 @@
+a/b/c

tests/data_fuzz_xpath/functions.xpath

@@ -0,0 +1 @@
+sum(nodes) + round(concat(//a[translate(@id, 'abc', '012')]))

tests/data_fuzz_xpath/math.xpath

@@ -0,0 +1 @@
+1+2*3 div 4 mod 5-6

tests/data_fuzz_xpath/path.xpath

@@ -0,0 +1 @@
+@*/ancestor::*/near-north/*[4]/@*/preceding::text()

tests/data_fuzz_xpath/predicate.xpath

@@ -0,0 +1 @@
+library/nodes[@id=12]/element[@type='translate'][1]

tests/fuzz_xpath.cpp

@@ -0,0 +1,26 @@
+#include "../src/pugixml.hpp"
+
+#include <stdint.h>
+#include <string.h>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
+{
+	char* text = new char[Size + 1];
+	memcpy(text, Data, Size);
+	text[Size] = 0;
+
+#ifdef PUGIXML_NO_EXCEPTIONS
+	pugi::xpath_query q(text);
+#else
+	try
+	{
+		pugi::xpath_query q(text);
+	}
+	catch (pugi::xpath_exception&)
+	{
+	}
+#endif
+
+	delete[] text;
+	return 0;
+}