[processing] fix Random extract/select within subset when subset is

smaller than number of requested features (fix #19322)

(cherry-picked from 29207a1)

Author: alexbruy

python/plugins/processing/algs/qgis/RandomExtractWithinSubsets.py

@@ -127,7 +127,7 @@ def processAlgorithm(self, parameters, context, feedback):
 
         for subset in classes.values():
             selValue = value if method != 1 else int(round(value * len(subset), 0))
-            selran.extend(random.sample(subset, selValue))
+            selran.extend(random.sample(subset, min(selValue, len(subset))))
 
         total = 100.0 / featureCount if featureCount else 1
         for (i, feat) in enumerate(selran):

python/plugins/processing/algs/qgis/RandomSelectionWithinSubsets.py

@@ -138,7 +138,7 @@ def processAlgorithm(self, parameters, context, feedback):
                     break
 
                 selValue = value if method != 1 else int(round(value * len(subset), 0))
-                selran.extend(random.sample(subset, selValue))
+                selran.extend(random.sample(subset, min(selValue, len(subset))))
 
             layer.selectByIds(selran)
         else:

python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

@@ -3923,6 +3923,21 @@ tests:
         name: points_weighted.gml
         compare: false
 
+  - algorithm: qgis:randomextractwithinsubsets
+    name: Random extract within subset (subset smaller than number)
+    params:
+      FIELD: id2
+      INPUT:
+        name: points.gml
+        type: vector
+      METHOD: 0
+      NUMBER: 3
+    results:
+      OUTPUT:
+        type: vector
+        name: points.gml
+        compare: false
+
   - algorithm: qgis:heatmapkerneldensityestimation
     name: Heatmap (Kernel density estimation)
     params:
@@ -5355,6 +5370,7 @@ tests:
         compare:
           fields:
             fid: skip
+
   - algorithm: native:difference
     name: Test Difference B - A (basic)
     params: