fmemopen.3: wfix

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/fmemopen.3

@@ -198,11 +198,11 @@ This byte is
 included in the size value stored at
 .IR sizeloc .
 
-The stream's file position can be changed with
+The stream's buffer position can be changed with
 .BR fseek (3)
 or
 .BR fseeko (3).
-Moving the file position past the end
+Moving the buffer position past the end
 of the data already written fills the intervening space with
 zeros.
 
@@ -322,7 +322,7 @@ since version 2.22, the glibc implementation provides that behavior.
 In versions of glibc before 2.22,
 specifying append mode ("a" or "a+") for
 .BR fmemopen ()
-sets the initial file position to the first null byte, but
+sets the initial buffer position to the first null byte, but
 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=13152
 (if the file offset is reset to a location other than
 the end of the stream)
@@ -338,12 +338,12 @@ specifies append ("a" or "a+"), and the
 argument does not cover a null byte in
 .IR buf ,
 then, according to POSIX.1-2008,
-the initial file position should be set to
+the initial buffer position should be set to
 the next byte after the end of the buffer.
 However, in this case the glibc
 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=13151
 .BR fmemopen ()
-sets the file position to \-1.
+sets the buffer position to \-1.
 This bug is fixed in glibc 2.22.
 
 In versions of glibc before 2.22,