some exception texts (#838)

src/exceptions/cx_sy_arithmetic_overflow.clas.abap

@@ -1,7 +1,14 @@
 CLASS cx_sy_arithmetic_overflow DEFINITION PUBLIC INHERITING FROM cx_sy_arithmetic_error.
 
+  PUBLIC SECTION.
+    METHODS if_message~get_text REDEFINITION.
+
 ENDCLASS.
 
 CLASS cx_sy_arithmetic_overflow IMPLEMENTATION.
 
+  METHOD if_message~get_text.
+    result = 'Arithmetic overflow'.
+  ENDMETHOD.
+
 ENDCLASS.

src/exceptions/cx_sy_conversion_no_number.clas.abap

@@ -1,7 +1,14 @@
 CLASS cx_sy_conversion_no_number DEFINITION PUBLIC INHERITING FROM cx_sy_conversion_error.
 
+  PUBLIC SECTION.
+    METHODS if_message~get_text REDEFINITION.
+
 ENDCLASS.
 
 CLASS cx_sy_conversion_no_number IMPLEMENTATION.
 
+  METHOD if_message~get_text.
+    result = 'Conversion no number'.
+  ENDMETHOD.
+
 ENDCLASS.

src/exceptions/cx_sy_range_out_of_bounds.clas.abap

@@ -1,7 +1,14 @@
 CLASS cx_sy_range_out_of_bounds DEFINITION PUBLIC INHERITING FROM cx_sy_data_access_error.
 
+  PUBLIC SECTION.
+    METHODS if_message~get_text REDEFINITION.
+
 ENDCLASS.
 
 CLASS cx_sy_range_out_of_bounds IMPLEMENTATION.
 
+  METHOD if_message~get_text.
+    result = 'Range out of bounds'.
+  ENDMETHOD.
+
 ENDCLASS.