x.json2: fix decode_number not initializing value to zero (fix #25641) (#25675)

Author: chethanyadav456

vlib/x/json2/decode.v

@@ -946,6 +946,7 @@ fn (mut decoder Decoder) decode_number[T](val &T) ! {
 		}
 
 		// doing it like this means the minimum of signed numbers does not overflow before being inverted
+		*val = 0 // initialize to zero before accumulating digits
 		if !is_negative {
 			digit_amount := get_number_digits(*val)
 

vlib/x/json2/tests/issue_25641_test.v

@@ -0,0 +1,29 @@
+import x.json2
+
+struct TestStruct {
+	age u16 = 25
+}
+
+fn test_u16_in_struct() {
+	original := TestStruct{}
+	encoded := json2.encode(original)
+	println('Encoded: ${encoded}')
+
+	decoded := json2.decode[TestStruct](encoded) or { panic('Failed to decode: ${err}') }
+	println('Decoded: ${decoded}')
+	println('Age value: ${decoded.age}')
+
+	assert decoded.age == 25, 'Expected age 25, got ${decoded.age}'
+}
+
+fn test_u16_direct() {
+	decoded := json2.decode[u16]('25') or { panic('Failed: ${err}') }
+	println('Direct u16 decode of "25": ${decoded}')
+	assert decoded == 25, 'Expected 25, got ${decoded}'
+}
+
+fn main() {
+	test_u16_direct()
+	test_u16_in_struct()
+	println('All tests passed!')
+}