fix doc

Author: PragmaTwice

mlir/include/mlir-c/Rewrite.h

@@ -103,7 +103,7 @@ mlirRewriterBaseGetBlock(MlirRewriterBase rewriter);
 
 /// Returns the operation right after the current insertion point
 /// of the rewriter. A null MlirOperation will be returned
-// if the current insertion block is empty.
+// if the current insertion point is at the end of the block.
 MLIR_CAPI_EXPORTED MlirOperation
 mlirRewriterBaseGetOperationAfterInsertion(MlirRewriterBase rewriter);