0027261: Incorrect bounding boxes computed for the b-spline faces

Protection from the out of bounds parameters is added.
Test cases are added.

src/BndLib/BndLib_AddSurface.cxx

@@ -195,6 +195,11 @@ void ComputePolesIndexes(const TColStd_Array1OfReal &theFlatKnots,
                          Standard_Integer &theOutMinIdx,
                          Standard_Integer &theOutMaxIdx)
 {
+  // Set initial values for the result indexes to handle situation when requested parameter space
+  // is slightly greater than B-spline parameter space.
+  theOutMinIdx = theFlatKnots.Lower();
+  theOutMaxIdx = theFlatKnots.Upper();
+
   // Compute first and last used flat knots.
   for(Standard_Integer aKnotIdx = theFlatKnots.Lower();
       aKnotIdx < theFlatKnots.Upper();

tests/bugs/moddata_3/bug27261_1

@@ -0,0 +1,15 @@
+puts "================"
+puts "0027261"
+puts "================"
+puts ""
+############################################################### 
+# Incorrect bounding box is created for the face
+##############################################################
+
+restore [locate_data_file bug27261_f1.brep] f1
+bounding f1
+
+# Visual check.
+smallview
+fit
+checkview -screenshot -2d -path ${imagedir}/${test_image}.png

tests/bugs/moddata_3/bug27261_2

@@ -0,0 +1,15 @@
+puts "================"
+puts "0027261"
+puts "================"
+puts ""
+############################################################### 
+# Incorrect bounding box is created for the face
+##############################################################
+
+restore [locate_data_file bug27261_f2.brep] f2
+bounding f2
+
+# Visual check.
+smallview
+fit
+checkview -screenshot -2d -path ${imagedir}/${test_image}.png