doc: Improve help text of osl_rbtree_first_row().HEADmaster

Shorten the text, improve its wording and mention that the function fails if
the table is empty.

1 files changed, 3 insertions, 4 deletions

diff --git a/osl.h.m4 b/osl.h.m4
index 1968975..320d9fd 100644
--- a/osl.h.m4
+++ b/osl.h.m4
@@ -505,10 +505,9 @@ DECLARE_FUNCTION(
 		«struct osl_row **result»,
 		«A pointer to the first row is returned here»
 	»,
-	«The rbtree node of the smallest object (with respect to the
-	corresponding compare function) is selected and the row containing
-	this object is returned. It is an error if col_num refers to a column
-	without an associated rbtree.
+	«Return a reference to the row whose object in the given column is smallest
+	with respect to the comparator of that column. It is an error if the table
+	is empty or if the given column has no associated red-black tree.
 
 	See also: osl_get_nth_row(), osl_rbtree_last_row().»,
 	«int»,