encoding: append `0` to strings for compatibility (#10249)

vlib/encoding/base64/base64.v

@@ -35,7 +35,8 @@ pub fn decode_str(data string) string {
 		return ''
 	}
 	unsafe {
-		buffer := malloc(size)
+		buffer := malloc(size + 1)
+		buffer[size] = 0
 		return tos(buffer, decode_in_buffer(data, buffer))
 	}
 }
@@ -61,7 +62,8 @@ fn alloc_and_encode(src &byte, len int) string {
 		return ''
 	}
 	unsafe {
-		buffer := malloc(size)
+		buffer := malloc(size + 1)
+		buffer[size] = 0
 		return tos(buffer, encode_from_buffer(buffer, src, len))
 	}
 }

vlib/rand/rand.v

@@ -197,12 +197,15 @@ pub fn string_from_set(charset string, len int) string {
 	if len == 0 {
 		return ''
 	}
-	mut buf := unsafe { malloc(len) }
+	mut buf := unsafe { malloc(len + 1) }
 	for i in 0 .. len {
 		unsafe {
 			buf[i] = charset[intn(charset.len)]
 		}
 	}
+	unsafe {
+		buf[len] = 0
+	}
 	return unsafe { buf.vstring_with_len(len) }
 }