fiber: extend name buffer on 1 byte for \0

Checks for fiber_name legth worked with FIBER_NAME_MAX,
while one byte in fact was occupied by terminating zero.

Closes #4011

src/fiber.h

@@ -417,7 +417,7 @@ struct fiber {
 	struct ipc_wait_pad *wait_pad;
 	/** Exception which caused this fiber's death. */
 	struct diag diag;
-	char name[FIBER_NAME_MAX];
+	char name[FIBER_NAME_MAX + 1];
 };
 
 enum { FIBER_CALL_STACK = 16 };

test/app/fiber.result

@@ -1186,7 +1186,7 @@ fiber = nil
 ---
 ...
 --
--- gh-2622 fiber.name() truncates new name
+-- gh-2622, gh-4011: fiber.name() truncates new name.
 --
 fiber = require('fiber')
 ---
@@ -1214,14 +1214,14 @@ fiber.name(long_name, {truncate = true})
 ...
 fiber.name()
 ---
-- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 ...
 f = fiber.self()
 ---
 ...
 fiber.name(f)
 ---
-- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 ...
 fiber.name(f, 'new_name')
 ---
@@ -1239,7 +1239,7 @@ fiber.name(f, long_name, {truncate = true})
 ...
 fiber.name(f)
 ---
-- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+- aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
 ...
 --
 -- gh-3493 fiber.create() does not roll back memtx transaction

test/app/fiber.test.lua

@@ -504,7 +504,7 @@ test_run:cmd("setopt delimiter ''");
 fiber = nil
 
 --
--- gh-2622 fiber.name() truncates new name
+-- gh-2622, gh-4011: fiber.name() truncates new name.
 --
 fiber = require('fiber')
 long_name = string.rep('a', 300)

test/unit/fiber.result

@@ -5,7 +5,7 @@ SystemError Failed to allocate 42 bytes in allocator for exception: Cannot alloc
 
 # set new fiber name: Horace.
 
-# fiber name is truncated: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.
+# fiber name is truncated: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.
 
 	*** fiber_name_test: done ***
 	*** fiber_join_test ***