Fix benchmark aggregation on different measured builds number

When scenarios have different iterations number, resulted csv file will
contain empty entries for some of the measurements. Aggregation should
ignore such entries.

libraries/tools/gradle/regression-benchmark-templates/src/main/kotlin/org/jetbrains/kotlin/gradle/benchmark/BenchmarkTemplate.kt

@@ -376,7 +376,7 @@ abstract class BenchmarkTemplate(
                 )
                 columnName.startsWith("measured build") -> DataColumn.createValueColumn(
                     columnName,
-                    rowToColumn(columnName) { it.toString().toInt() }
+                    rowToColumn(columnName) { it.toString().toIntOrNull() }
                 )
                 else -> throw IllegalArgumentException("Unknown column name: $columnName")
             }