Fix IOBuffer skip regression (#57963)

Fixes #57962

This reverts the changes to `skip` added in #57570

The code before #57570 was written in a very specific way to avoid
overflow errors, so I'm not sure why this was changed.

(cherry picked from commit b29c808)

Author: nhz2

base/iobuffer.jl

@@ -486,8 +486,8 @@ function skip(io::GenericIOBuffer, n::Int)
     else
         # Don't use seek in order to allow a non-seekable IO to still skip bytes.
         # Handle overflow.
-        maxptr = io.size + 1
-        io.ptr = n > maxptr || io.ptr - n > maxptr ? maxptr : io.ptr + n
+        n_max = io.size + 1 - io.ptr
+        io.ptr += min(n, n_max)
         io
     end
 end

test/iobuffer.jl

@@ -497,6 +497,13 @@ end
     end
 end
 
+@testset "issue #57962" begin
+    io = IOBuffer(repeat("x", 400))
+    skip(io, 10)
+    skip(io, 400)
+    @test isempty(read(io))
+end
+
 @testset "pr #11554" begin
     io  = IOBuffer(SubString("***αhelloworldω***", 4, 16))
     io2 = IOBuffer(Vector{UInt8}(b"goodnightmoon"), read=true, write=true)