fix: split if statement, the compond logical condition does not get e…

…ntered

and gives a 'Failed to converge for quantile' when quantile==0
see issue #709

Q. Is this a floating point comparison error? (plus short circuting the if statement)

assimilation_code/modules/assimilation/normal_distribution_mod.f90

@@ -360,13 +360,22 @@ function first_guess(quantile, p)
 endif
 
 ! If the distribution is bounded, quantiles at the limits have values at the bounds
-if(bounded_below .and. quantile == 0.0_r8) then
-   x = lower_bound
-   return
+if(quantile == 0.0_r8) then
+   ! The following statement is required to avoid a compiler bug in gcc 13.2.0
+   quantile = 0.0_r8
+   if(bounded_below) then
+      x = lower_bound
+      return
+   endif
 endif
-if(bounded_above .and. quantile == 1.0_r8) then
-   x = upper_bound
-   return
+
+if(quantile == 1.0_r8) then
+   ! The following statement is required to avoid a compiler bug in gcc 13.2.0
+   quantile = 1.0_r8
+   if(bounded_above) then
+      x = upper_bound
+      return
+   endif
 endif
 
 ! If input quantiles are outside the numerically supported range, move them to the extremes