Removing zeroing of trailing space in attribute buffers

This was provided as a courtesy to hopefully make custom attributes more
easy to use, however the zeroing turned out to be a bit complicated when
syncing custom attributes across multiple open files.

Implicitly zeroing trailing buffer space is also inconsistent with the
other APIs in the filesystem, such as lfs_file_read, so this commit
removes the behavior.

If you need to handle differently sized custom attributes, you can
either pre-zero the custom attribute buffers, or use lfs_getattr to find
the on-disk size of custom attributes explicitly.

tests/test_paths.toml

@@ -95,9 +95,9 @@ code = '''
 
     lfs_mkdir(&lfs, "coffee/../milk") => 0;
     lfs_stat(&lfs, "coffee/../milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_stat(&lfs, "milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -129,9 +129,9 @@ code = '''
     lfs_mount(&lfs, &cfg) => 0;
     lfs_mkdir(&lfs, ".milk") => 0;
     lfs_stat(&lfs, ".milk", &info) => 0;
-    strcmp(info.name, ".milk") => 0;
+    assert(strcmp(info.name, ".milk") == 0);
     lfs_stat(&lfs, "tea/.././.milk", &info) => 0;
-    strcmp(info.name, ".milk") => 0;
+    assert(strcmp(info.name, ".milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -149,13 +149,13 @@ code = '''
     lfs_mkdir(&lfs, "coffee/coldcoffee") => 0;
 
     lfs_stat(&lfs, "coffee/../../../../../../tea/hottea", &info) => 0;
-    strcmp(info.name, "hottea") => 0;
+    assert(strcmp(info.name, "hottea") == 0);
 
     lfs_mkdir(&lfs, "coffee/../../../../../../milk") => 0;
     lfs_stat(&lfs, "coffee/../../../../../../milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_stat(&lfs, "milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''