rational: assert when limits are used for calculations

These will necessarily result in overflows or underflows so I've attempted to weed this behavior out while adding asserts in case there are still usages I haven't found

app/common/rational.cpp

@@ -186,6 +186,8 @@ const rational& rational::operator=(const rational &rhs)
 
 const rational& rational::operator+=(const rational &rhs)
 {
+  Q_ASSERT(*this != RATIONAL_MIN && *this != RATIONAL_MAX && rhs != RATIONAL_MIN && rhs != RATIONAL_MAX);
+
   if (!isNaN()) {
     if (rhs.isNaN()) {
       // Set to NaN
@@ -209,6 +211,8 @@ const rational& rational::operator+=(const rational &rhs)
 
 const rational& rational::operator-=(const rational &rhs)
 {
+  Q_ASSERT(*this != RATIONAL_MIN && *this != RATIONAL_MAX && rhs != RATIONAL_MIN && rhs != RATIONAL_MAX);
+
   if (!isNaN()) {
     if (rhs.isNaN()) {
       // Set to NaN
@@ -232,6 +236,8 @@ const rational& rational::operator-=(const rational &rhs)
 
 const rational& rational::operator/=(const rational &rhs)
 {
+  Q_ASSERT(*this != RATIONAL_MIN && *this != RATIONAL_MAX && rhs != RATIONAL_MIN && rhs != RATIONAL_MAX);
+
   if (!isNaN()) {
     if (rhs.isNaN()) {
       // Set to NaN
@@ -250,6 +256,8 @@ const rational& rational::operator/=(const rational &rhs)
 
 const rational& rational::operator*=(const rational &rhs)
 {
+  Q_ASSERT(*this != RATIONAL_MIN && *this != RATIONAL_MAX && rhs != RATIONAL_MIN && rhs != RATIONAL_MAX);
+
   if (!isNaN()) {
     if (rhs.isNaN()) {
       denom_ = 0;

app/common/rational.h

@@ -1,7 +1,7 @@
 //Copyright 2015 Adam Quintero
 //This program is distributed under the terms of the GNU General Public License.
 
-// Adapted by MattKC for the Olive Video Editor (2019)
+// Adapted by MattKC for the Olive Video Editor (2019-2022)
 
 #ifndef RATIONAL_H
 #define RATIONAL_H

app/common/timerange.cpp

@@ -44,6 +44,7 @@ const rational &TimeRange::out() const
 
 const rational &TimeRange::length() const
 {
+  Q_ASSERT(!length_.isNaN());
   return length_;
 }
 
@@ -173,7 +174,11 @@ void TimeRange::normalize()
   }
 
   // Calculate length
-  length_ = out_ - in_;
+  if (out_ == RATIONAL_MIN || out_ == RATIONAL_MAX || in_ == RATIONAL_MIN || in_ == RATIONAL_MAX) {
+    length_ = rational::NaN;
+  } else {
+    length_ = out_ - in_;
+  }
 }
 
 void TimeRangeList::insert(const TimeRangeList &list_to_add)