继续按 align-linuxcnc 约束：补 O-word 调用错误源码覆盖，测试通过

test-linuxcnc-source-link.sh

@@ -874,8 +874,9 @@ if CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
     exit 1
 fi
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc read_o()
-# and read_items() reject malformed O-word control lines and Fanuc-style
-# M98 calls before execution.
+# and read_items() reject malformed O-word control lines, empty call
+# parameter expressions through read_real_expression()/read_real_number(),
+# and Fanuc-style M98 calls before execution.
 oword_reader_error_cases=(
     "linuxcnc_oword_unknown_command_error|Unknown control command in o word"
     "linuxcnc_oword_unexpected_trailing_item_error|Unexpected character after O-word"
@@ -884,6 +885,7 @@ oword_reader_error_cases=(
     "linuxcnc_oword_while_missing_bracket_error|Left bracket missing after 'while'"
     "linuxcnc_oword_repeat_missing_bracket_error|Left bracket missing after 'repeat'"
     "linuxcnc_oword_too_many_call_parameters_error|Too many subroutine parameters"
+    "linuxcnc_oword_empty_call_parameter_error|bad number format (conversion failed) parsing ''"
     "linuxcnc_m98_missing_p_word_error|Found 'm98' code with no P-word"
     "linuxcnc_comment_prefixed_m98_error|Unknown m code used: M98"
 )
@@ -919,6 +921,7 @@ oword_execution_error_cases=(
     "linuxcnc_oword_endwhile_no_matching_while_error|no matching label"
     "linuxcnc_oword_fanuc_requires_m99_error|Fanuc 'O....' subroutine definition must end with 'M99'"
     "linuxcnc_oword_sub_requires_endsub_error|'O.... endsub' or 'O.... return' must follow 'O.... sub'"
+    "linuxcnc_oword_too_many_call_levels_error|Too many subroutine levels"
 )
 for case in "${oword_execution_error_cases[@]}"; do
     fixture=${case%%|*}