Fix: species_type init memory (#5119)

The `PC::physical_species` was undefined memory unless
`<species_name>.species_type` was provided in the input set.
This initializes this member variable to a clear
`PhysicalSpecies::unspecified` instead of random memory, which
caused UB in functions such as `IamA<...>` during I/O.

Source/Particles/WarpXParticleContainer.H

@@ -433,7 +433,7 @@ protected:
 
     amrex::ParticleReal charge;
     amrex::ParticleReal mass;
-    PhysicalSpecies physical_species;
+    PhysicalSpecies physical_species = PhysicalSpecies::unspecified;
 
     // Controls boundaries for particles exiting the domain
     ParticleBoundaries m_boundary_conditions;