StringReader off-by-one panic

[daddycocoaman]

Describe the bug

When attempting to read one byte at the end of the buffer with StringReader, V will panic. This is because the StringReader.needs_fill_until and StringReader.needs_fill will return true if the requested length is equal to or greater than the length of the buffer. The buffer should only be filled if the requested length is greater than the length of the buffer, not equal to.

Reproduction Steps

import io.string_reader

fn main() {

    source := "ABCD"
	mut reader := string_reader.StringReader.new(source: source)

	println(reader.read_all_bytes(true)!)

	reader = string_reader.StringReader.new(source: source)
        println(reader.read_bytes(1)!)
	println(reader.read_bytes(1)!)
	println(reader.read_bytes(1)!)
	println(reader.read_bytes(1)!)
}

Expected Behavior

StringReader will read the last byte of the buffer if the length to read requested is equal to the end of the buffer.

Current Behavior

[65, 66, 67, 68]
[65]
[66]
[67]
V panic: result not set (reader is not set)
v hash: a867ed6
print_backtrace_skipping_top_frames is not implemented

Possible Solution

I actually don't understand why the reader object disappears in the fill_buffer functions. Even if the buffer is at the end of the stream and too many bytes are requested, shouldn't it still be there? At any rate, the needs_fill functions should probably be changed to check for only greater than, not greater than or equal to.

Additional Information/Context

No response

V version

V 0.4.4 f789874.a867ed6

Environment details (OS name and version, etc.)

V full version: V 0.4.4 f789874.a867ed6
OS: windows, Microsoft Windows 11 Enterprise v26058 ARM 64-bit Processor
Processor: 8 cpus, 64bit, little endian, 

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