Throw an exception when an implicit narrowing conversion in a compound

assignment would result in information loss or a numeric error such as
an overflows.

src/changes/changes.xml

@@ -67,6 +67,8 @@ The <action> type attribute can be add,update,fix,remove.
     <action                   type="fix" dev="kinow" due-to="Roland Kreuzer">Javadoc for StringUtils.substringBefore(String str, int separator) doesn't mention that the separator is an int.</action>
     <action                   type="fix" dev="ggregory" due-to="Gary Gregory">Fix NullPointerException in ThreadUtils.getSystemThreadGroup() when the current thread is stopped.</action>
     <action                   type="fix" dev="ggregory" due-to="Gary Gregory">ArrayUtils.toPrimitive(Boolean...) null array elements map to false, like Boolean.parseBoolean(null) and its callers return false.</action>
+    <action                   type="fix" dev="ggregory" due-to="CodeQL, Gary Gregory">Throw an exception when an implicit narrowing conversion in a compound assignment would result in information loss or a numeric error such as an overflows.</action>
+    
     <!-- ADD -->
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add EnumUtils.getEnumSystemProperty(...).</action>
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add TriConsumer.</action>

src/main/java/org/apache/commons/lang3/text/StrBuilder.java

@@ -2985,7 +2985,7 @@ public class StrBuilder implements CharSequence, Appendable, Serializable, Build
             if (n < 0) {
                 return 0;
             }
-            pos += n;
+            pos = Math.addExact(pos, Math.toIntExact(n));
             return n;
         }