JIT: don't allow negative edge weights (#56651)

Due to rounding errors or inconsistencies we may end up with unexpected
ratios of profile counts. Fix one place where that was leading to a negative
edge weight.

Fixes #56647.

src/coreclr/jit/fgprofile.cpp

@@ -3000,6 +3000,8 @@ bool flowList::setEdgeWeightMaxChecked(BasicBlock::weight_t newWeight,
 void flowList::setEdgeWeights(BasicBlock::weight_t theMinWeight, BasicBlock::weight_t theMaxWeight, BasicBlock* bDst)
 {
     assert(theMinWeight <= theMaxWeight);
+    assert(theMinWeight >= 0.0f);
+    assert(theMaxWeight >= 0.0f);
 
     JITDUMP("Setting edge weights for " FMT_BB " -> " FMT_BB " to [" FMT_WT " .. " FMT_WT "]\n", getBlock()->bbNum,
             bDst->bbNum, theMinWeight, theMaxWeight);

src/coreclr/jit/optimizer.cpp

@@ -4467,7 +4467,7 @@ bool Compiler::optInvertWhileLoop(BasicBlock* block)
         // Note "next" is the loop top block, not bTest's bbNext,
         // we'll call this latter block "after".
         //
-        BasicBlock::weight_t const testToNextLikelihood  = weightNext / weightTest;
+        BasicBlock::weight_t const testToNextLikelihood  = min(1.0f, weightNext / weightTest);
         BasicBlock::weight_t const testToAfterLikelihood = 1.0f - testToNextLikelihood;
 
         // Adjust edges out of bTest (which now has weight weightNext)